The 45-year-old actress took to Instagram on Friday to share a candid photo of herself wearing a white T-shirt that repeated the name "Mahsa Amini" in red letters, drawing attention to the 22-year-old woman who died in Iran in September.
Styled by Elizabeth Stewart, Chastain wore the eye-catching top in New York's Upper West Side on Wednesday, pairing the shirt with a brown blazer, matching pants and black Christian Louboutin red-sole heels.
"It's been over two months since the death of Mahsa Amini," Chastain began the caption to her post. "Over two months of nationwide protests in Iran. Over two months of the regime's violent crackdown, killing women, men and children who are fighting for freedom. Stand with Iran. Use your voice."
The "Good Nurse" and "Interstellar" star continued to share two ways people can show their support: By sharing any posts about what's happening in Iran to "spotlight the atrocities," and by signing petitions.
Fans were quick to say thanks and show their appreciation for Chastain for using her platform wisely.
"You are always on the right side of history," one person wrote, along with a white heart emoji.
"You don't just talk, you act. You use your platform to make visible what's happening in the world. You fight for women rights!" penned a fan.
"Thank you for sharing your kind heart and soul, and for using your platform and voice for the voiceless. You are such a genuinely selfless soul," another added.
"Couldn't possibly love you more," someone chimed in.
"You are truly incredible. Thank you for using your voice to help the innocent people of Iran," someone else shared. "You're doing way more than many Iranian public figures who have shut their mouth against the brutalities of this regime."
The brand, founded by Toronto-native designer Joey Gollish, said it wanted to "work alongside them in a collective effort to spread awareness about the Islamic Republic regime's violent crackdown on the women, men and children fighting for their freedom."
"We stand with the people of Iran and urge you to use your voice to put a spotlight on the atrocities happening right now," the brand added in their post.
In September, Chastain also used her platform on Instagram to spread awareness of Amini's death. The "Eyes of Tammy Faye" and "Scenes From a Marriage" star shared a carousel of photos from the protests that occurred that month.
"Mahsa Amini is an Iranian woman who was beaten to death last week in a 're-education centre' for not wearing her hijab correctly," Chastain began in an Instagram post made on Sept. 25. "Her death lead to thousands of Iranians taking to the streets, demanding an end to violence and discrimination against women. Dozens of these protesters have been killed.
"But the people of Iran will not be silenced. I stand with the women of Iran and will amplify their voices from afar. When one woman is attacked, it is an attack on us all."