Chastain, 46, appeared in Venice, Italy, Friday to support her movie Memory at the festival wearing a T-shirt that read "SAG-AFTRA ON STRIKE."
Though Screen Actors Guild members are generally prohibited from promoting their current or past projects during the strike, Chastain was able to appear at the festival because Memory is an independent production that obtained an interim agreement from the guild.
“I was incredibly nervous to be here today and to come here, and actually there are some people on my team who advised me against it," the Oscar winner said during a press conference when asked if she "hesitated" to attend.
"We [actors] are often told and reminded how grateful we should be," she told reporters. "And that is the environment that I think has allowed workplace abuse to go unchecked for many decades and is also the environment that has saddled members of our union with unfair contracts."
Chastain echoed Ferrari actor Adam Driver's words earlier this week at Venice as she noted that her presence at the festival, given Memory's interim agreement, is important to the guild's strategy in ending the strike, which began July 13.
"It’s what our national board, negotiating committee and our elected leadership has asked us to do," she said. "And when independent producers like the ones here of these films sign these interim agreements, they are letting the world know, letting the AMPTP know that actors deserve fair compensation, that AI protection should be implemented, and there should be sharing of streaming revenue."
Chastain stars with Peter Sarsgaard, who was also in Venice Friday, in Memory. The film follows a social worker named Sylvia whose life "is blown open when Saul (Sarsgaard) follows her home from their high school reunion," according to an official synopsis for the film.
"Their surprise encounter will profoundly impact both of them as they open the door to the past," the synopsis adds.
“I’ve always wanted to work with Peter. We’ve met a few times before this and we’ve talked about it. I’ve not been hidden in my fanship of his movies and who he is as an actor," Chastain said during the press conference.
"He’s a real artist. Sometimes an actor will change the script or the story to fit them, and the best is when you change yourself to fit the story. He’s a shape-shifter, so it was a big pleasure."
Memory makes its world premiere in Venice on Friday. It will also premiere at the Toronto International Film Festival on Sunday.