The alpaca’s scream sounded like a high-pitched electric pencil sharpener, more machine than mammal. It was awful, and that was the point. The group behind the video, People for the Ethical Treatment of Animals, has been publicizing graphic scenes like this long enough to know which sights and sounds make people feel the most miserable.

This footage was filmed during an “undercover investigation” at a Peruvian farm, the group said, and shown to The New York Times recently, before being released more widely. It’s part of PETA’s latest project: ridding the world of alpaca sweaters. That means agitating the people who wear them, the retailers who sell them and the manufactures who make them.

PETA’s mode of making social change has always been to inspire shock and ignite boycotts. For years, we’ve watched videos of screaming animals and seen red paint splatter fur coats. With these in-your-face and highly visual tactics, the activists helped win the culture war over fur.

But it’s been 15 years now since Anna Wintour was last dealt a tofu pie to the face.

Behind closed doors, PETA has embarked on a mission of corporate diplomacy. These days, much of its activism involves organizing conference calls and sending forceful but respectful emails. Supporters don’t flood the streets as often as they flood Twitter. The famously loud group, now 40 years old, is operating more quietly. More brands than ever are listening.

“We’re no longer storming the offices of fashion companies,” said Laura Shields, the corporate responsibility manager at PETA. “Now we’re getting invited to come sit down at the boardroom table.”

How PETA Enacts Its Influence in Private

One aspect of PETA’s activism has not changed: There must be a villain. Before an investigation goes public, it’s the job of Ms. Shields’s team to make a list of candidates.

Typically, this happens after PETA’s investigations department has identified an industry (like angora wool) or an individual supplier (like a factory) suspected of abusing animals, and gathered supporting footage. The corporate responsibility team then determines which brands use the supplier or support that industry.

Ms. Shields, 37, said that when choosing a target, PETA considers how much animal material is being sold by the company, whether the company can influence others and whether the company’s core market has strong feelings about animals. (The more young female customers, the better.) Last year, for example, targets included Nordstrom (for fur) and Madewell (for cashmere).

It’s a single-minded, black-and-white approach, as extreme as the activists’ trademark nudity or hyperbolic language, even if not as showy. It doesn’t matter to PETA if a company makes a good-faith pledge to source responsibly or phase out certain products over time. If it’s still selling animals, it’s still a mark.

At the end of 2019, as the corporate responsibility team mulled over the alpaca investigation, its potential targets were narrowed down to H&M, Gap and Anthropologie. The three brands were all reasonably likely to consider an alpaca ban; during a previous PETA campaign, each had promised to stop selling mohair products.

On Dec. 9, PETA sent emails to the three companies. H&M and Gap were warned that a “highly confidential investigation” into alpaca was coming, and they were asked to meet right away.

H&M responded the next day, according to emails provided by a PETA official. The company said it was “so grateful” that PETA had reached out and given it “the opportunity to act if needed.”

By the end of January, H&M and Gap had spoken to PETA over video chat, exchanged emails with the group, received video of the writhing and wailing Peruvian alpacas and come to the same decision: They would not use the farm’s parent company as a supplier in the future.

A Gap representative explained the company’s reasoning in an email to PETA, writing that it was “a result of business decisions that were already underway, and influenced by the findings from the investigation.” The representative added: “Personally, I was heartbroken to watch the video and want you to know that this has been a top priority.”

To PETA’s disappointment, however, neither company would commit to banning alpaca outright. (“Sorry for not having a more happy reply to send you this Friday,” the H&M representative wrote.)

When asked about how decisions like these are made, H&M’s sustainability expert, Madelene Ericsson, said the company wants to use animal materials only when “we believe we can actually make a change for the animals” — meaning to “only source from good farms.” A representative for Gap did not respond to The Times before publication.

PETA’s attempts to sway Anthropologie went a little differently.

In its Dec. 9 email, PETA told Anthropologie executives it wanted to give them “the opportunity to do right before we launch this new investigation.”

“In the past, PETA has found it impactful to approach retailers before publicizing new investigations,” the group wrote, so that brands could “get ahead of the issue and be praised for taking corrective actions, rather than having to scramble after-the-fact.”

This message was more pointed than those sent to H&M and Gap, in part because while Anthropologie did ban mohair in 2018, it did not announce that decision until the day after PETA urged followers to protest Anthropologie. If the company worked with PETA now, before the alpaca video went public, it wouldn’t be called out like that again.

Anthropologie did not respond to the email, PETA said, or to follow-up messages. (Urban Outfitters, the parent company of Anthropologie, declined to speak to The New York Times for this article.)

With that, PETA found its target.

Because of that lack of response, PETA plans to issue an “action alert” on Anthropologie, instructing supporters to send Anthropologie pre-written emails — using one of PETA’s online tools — pleading that the company “think of gentle alpacas.”

In the meantime, PETA will publicly highlight H&M and Gap for cutting ties with the Peruvian farm.

When PETA Needed the Media

When Tracy Reiman, the executive vice president of PETA, considers the group’s legacy, she thinks about a day in January 1994, when she and her colleagues stormed the offices of Calvin Klein, yelling and spray-painting the walls until seven of them were arrested.

Afterward, Mr. Klein agreed to a meeting with PETA, watched a graphic video and subsequently announced he would no longer sell fur. The activists declared victory, though the designer later said he made his decision before the raid. (Furriers cast doubt on this claim.)

“For me, it reinforced how PETA’s pushy style can really force change quickly,” said Ms. Reiman, 52, calling the Klein protest a “watershed moment.”

Throughout the 1990s, the war on fur raged on; sometimes it seemed as if activists had the upper hand, until fur sales rebounded or until magazines or designers revived the trend. In the 2000s, PETA continued to disrupt runway shows and flour-bomb celebrities.

Fur supporters fought back. After the 2005 tofu pie incident, when Ms. Wintour was asked how she would respond, she reportedly answered: “Wear more fur.” But PETA’s rhetoric was always more heated and vengeful.

After Cindy Crawford and Naomi Campbell, who’d posed nude in a 1994 anti-fur ad that raised PETA’s national profile, were seen wearing fur again, PETA called Ms. Crawford “desperate” and Ms. Campbell a “disgrace,” suggesting her change in heart was a result of her “taking” something. (Ms. Campbell has said she sought treatment for addiction in 1997.)

In 2003, Ingrid Newkirk, the PETA founder, attributed its extreme language to being “complete press sluts.” At the time, the organization depended heavily on the media to cover its behavior and make its causes known. It doesn’t anymore.

“We would work very hard to get an eight-second clip from one of our videos on the news at night, which was nearly impossible because it was so graphic,” Ms. Reiman said. “Now we’ll put it on Facebook or Instagram, and millions of people will see it within 24 hours.”

That doesn’t mean PETA has abandoned stunts. Most recently, the organization erected billboards that connected the origin of the coronavirus with meat: “Tofu never caused a pandemic. Try it today!” And it still tries to use the press to amplify its causes. (Which is why it will likely release its alpaca investigation to the public right after this article is published.)

Now the power and ease of social media — the way it fuels call-out culture — is one reason “we don’t have to get arrested or push the envelope too far,” Ms. Reiman said. “In the early days, we’d have to fight for two years to win a campaign. These days we tend to win within hours.”

Today PETA works behind the scenes with hundreds of retail companies, Ms. Reiman added, though a few refuse to publicly acknowledge the activists, and others completely ignore them. Some of these dealings are even warm (see: Gap and H&M), in a sterile kind of way.

Still, no matter how good the relationship with a company, Ms. Reiman said, PETA won’t hesitate to put a brand on blast if its requests are ignored or rejected.

“Many companies respect us for it, or perhaps they fear us,” she said, “but either way they talk to us.”

What Changed? We Did.

While a handful of major designers eliminated fur before 2010 — Ralph Lauren, Tommy Hilfiger, Stella McCartney and Vivienne Westwood, among others — the real cease-fire began when the Italian luxury houses went fur free.

Armani announced in 2016, followed by Gucci in 2017, Versace in 2018 and Prada in 2019. Fendi, which popularized “fun fur” under its former creative director Karl Lagerfeld, has notably held on to its skins.

Fur-free brands now include fast-fashion companies (Asos and Zara), outdoor retailers (the North Face and Timberland) and high-end e-commerce platforms (Net-a-Porter and Farfetch). The state of California has banned fur sales entirely. Even PETA’s current fashion nemesis, Canada Goose, has stepped (slightly) away from fur.

PETA is not the only organization appealing to brands on the corporate level. PJ Smith, the fashion policy director at the Humane Society of the United States, has spent the last decade working on fur bans, including with several of the same luxury brands.

At first it was difficult to get meetings, Mr. Smith said. As he tells it, a wall had been erected between activists and the clothing industry, largely because of PETA’s past provocations. Once, he recalled, he went to meet with a company’s executive staff and was greeted at the door by a retired police officer. “They thought I was going to show up with a bucket of blood and a sign,” he said.

Around 2005, when the Humane Society began working with retailers on legislation requiring clear labeling of fur — trying to prevent real fur from being sold as faux — the wall started coming down. Mr. Smith gradually learned not to open meetings by showing companies images of animals in pain; it was more effective to send links.

When asked if he thought animal activists’ approach or the industry’s response had changed more, Mr. Smith said neither. Shoppers changed. They started caring more about fashion’s environmental footprint, particularly younger consumers. Animals were part of that. A 2019 luxury market report by the Boston Consulting Group found that 36 percent of Gen Z respondents chose animal care as their most valued aspect of sustainability.

Brands suddenly saw the marketing potential in going fur free, Mr. Smith said. Most of these brands didn’t sell much fur anyway. (Leather and exotic skins — which only a few companies have pledged to stopped using — were another story.) When Gucci announced its fur ban on Instagram, it became the brand’s most liked post that didn’t have Harry Styles in it.

“Now there’s almost this competition,” Mr. Smith said. “Everyone wants to be a leader.”

One of these contenders, H&M, has had an animal welfare and material ethics policy in place since 2004, Ms. Ericsson said.

Maintaining a “close dialogue” with organizations including PETA has become an important part of this policy, Ms. Ericsson said: “We share the same view that no animals should be harmed in the name of fashion.”

Sharing this view may be a radical shift from PETA’s more notorious years, when fashion executives openly called the group “thoroughly obnoxious,” and when it “had to beg, steal and borrow” attention, said Lisa Lange, the senior vice president for communications of PETA, who has worked there for 28 years.

But supporters don’t seem to mind the taming of PETA. In 2019, the organization’s contributions hit $49.1 million, more than triple the contributions in 2000 — the height of the era of throwing paint and pies. Playing (sort of) nice is working for PETA.

“We’re not knives out instantly,” Ms. Lange said. “That’s something I think people don’t know. There is a lot of communicating that goes on before the knives come out.”