The letter, signed by five people and addressed to Ann Sarnoff, who took over as Warner’s chief executive last month, concluded by pressing the studio to join companies like CVS and Walmart in more fully embracing gun safety. The letter asked Warner to end political contributions to candidates who take money from the National Rifle Association, to lobby for gun reform, and to give money to survivor funds and gun violence intervention programs.

“We are calling on you to be a part of the growing chorus of corporate leaders who understand that they have a social responsibility to keep us all safe,” the letter said.

Sandy Phillips, whose daughter was among the 12 killed in Aurora in 2012, signed the letter and spoke more pointedly in an interview.

“If it’s one person that is excited or encouraged to become violent from seeing something like that, then that’s one too many,” she said. “Who are we to say that somebody in that audience isn’t a wannabe mass shooter and isn’t encouraged by what he’s seen onscreen?”

Warner has been consistently daring in its handling of screen violence, going back to the 1930s with sharp-edged gangster movies like “Little Caesar” and “The Public Enemy.” The most contentious Warner entries include Stanley Kubrick’s “A Clockwork Orange” (1971), which the director had pulled from theaters in Britain after it seemed to prompt copycat incidents; “Natural Born Killers” (1994), which generated headlines and a lawsuit for supposedly inspiring crimes similar to those committed by the film’s protagonists; and “The Matrix” (1999), which became linked in the news media to the massacre at Columbine High School in Colorado.

Igor Volsky, executive director of the advocacy group Guns Down America, helped write the letter that was sent to Warner on Tuesday. He said in a telephone interview that he had not seen “Joker.” He said the trailer and online reactions to festival screenings had prompted the letter.

He added that he agreed with the studies that had shown no direct link between violence in movies and violence in the real world.

“Everyone else in our peer countries see the same movies and play the same video games, yet we are the ones with the high rates of violence,” he said. “The reason for that is that guns in America are way too easy to get. That is the source of the problem, and that’s what we are asking companies to do: Help build safer communities with fewer guns.”