Relatives of people killed in the 2012 shooting at a theater in Aurora, Colorado, during a Batman movie are expressing unease about “Joker,” an upcoming film that has divided critics with its dark, violent take on the comic book villain.

In a letter to the film’s distributor, Warner Bros., the five family members call on the studio to end contributions to political candidates who accept money from the National Rifle Association, to lobby for gun reforms in Congress and to donate to organizations that help survivors of gun violence.

“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 says, according to a copy shared with NBC News on Tuesday by the group Guns Down America, which worked with the five signatories on the statement.

The letter stops short of calling on Warner Bros. to cancel plans to release “Joker,” which stars Oscar-nominated actor Joaquin Phoenix as a troubled, twisted stand-up comedian who turns to brutal violence in Gotham City, eventually becoming Batman’s arch-nemesis.

“When we learned that Warner Bros. was releasing a movie … that presents the character as a protagonist with a sympathetic origin story, it gave us pause,” the letter says.

“We want to be clear that we support your right to free speech and free expression. But as anyone who has ever seen a comic book movie can tell you: with great power comes great responsibility,” the letter adds, quoting a line from the 2002 adaptation of “Spider-Man.”

Warner Bros., which owns the DC Comics brand, did not immediately respond to a request for comment. (The letter is addressed to Warner Bros. CEO Ann Sarnoff.) The film’s director, Todd Phillips — best known for raunchy comedies like “The Hangover” trilogy — did not immediately respond to a request for comment.

The letter was signed by:

• Sandy and Lonnie Phillips, whose 24-year-old daughter, Jessica Ghawi, was killed in the shooting.
• Theresa Hoover, whose 18-year-old son, Alexander J. Boik, was killed.
• Heather Dearman, whose cousin, Ashley Moser, lost a 6-year-old daughter and unborn child.
• Tina Coon, whose son was a witness to the massacre.

The news, coming after a spate of mass shootings in the U.S., was first reported by The Hollywood Reporter.

“Joker,” slated for theatrical release on Oct. 4, stirred debate after it won the top prize at the Venice International Film Festival in August, drawing plaudits for Phoenix’s performance as the sadistic antihero and denunciation for its gritty depiction of his descent into madness.

The trailers for “Joker” contain clear allusions to the Martin Scorsese classics “Taxi Driver” and “The King of Comedy,” two films in which Robert De Niro — who plays a supporting role in “Joker” — portrayed alienated social outcasts driven to violence.

In a review published Aug. 31, Indiewire film critic David Ehrlich called the the R-rated project “a true original that’s sure to be remembered as one of the most transgressive studio blockbusters of the 21st Century.”

Ehrlich then expressed concern about the film’s real-world implications, writing that it was “a toxic rallying cry for self-pitying incels,” shorthand for the online community of misogynists who identify as involuntary celibates.

Phoenix, who could earn his fourth Academy Award nomination for his raw performance, reportedly walked out of a recent interview after he was asked by a journalist if he felt “Joker” might inspire real acts of violence.

In an interview with IGN published this week, Phoenix appeared to defend the film, saying: “I think that, for most of us, you’re able to tell the difference between right and wrong. I don’t think it’s the responsibility of a filmmaker to teach the audience morality or the difference between right or wrong. I mean, to me, I think that that’s obvious.

The film comes as major Hollywood studios, keen to put fresh spins on familiar characters and long-running franchises, experiment with hard-edged visual styles and more mature themes, such as in the R-rated X-Men thriller “Logan” and the somber action drama “War for the Planet of the Apes.”

The shooting in Aurora killed 12 people and wounded 70 others, including 58 from gunfire. The gunman, James Holmes, carried out the attack during a midnight showing of Christopher Nolan’s “The Dark Knight Rises,” part of a trilogy that was itself a gritty reboot of the original Batman saga, in the Denver suburb on July 20, 2012.

“I don’t need to see a picture of [Holmes],” Sandy Phillips, mother of Aurora victim Jessica Ghawi, told The Hollywood Reporter. “I just need to see a ‘Joker promo’ and I see a picture of the killer.”

“My worry is that one person who may be out there — and who knows if it is just one — who is on the edge, who is wanting to be a mass shooting, may be encouraged by this movie,” Phillips added. “And that terrifies me.”