Jessica Chastain ''cares more'' about Octavia Spencer's salary than her own.

The 41-year-old actress was horrified when she learned how much the Oscar-winning star had been offered for an upcoming project they are to star in together, but helped Octavia negotiate a salary five times higher than her original offer because of her passionate belief in ''equal pay for equal work''.

She said: ''I knew women of colour got paid less than Caucasian actresses.

''What I didn't know is someone of Octavia's level, who had an Oscar and two Oscar nominations, how much less she would be getting paid.

''When she told me what she was making, that's what really made me go, 'Hold up, that doesn't compute in my brain.'...

''This is the God's honest truth -- I care more about what Octavia's getting paid than what I'm getting paid. Because I've got a great life. I am more concerned about her than I am about me. Equal pay for equal work!''

And Octavia hailed her friend as her ''biggest cheerleader'' and ''most vocal advocate''.

She said: ''I shared a personal story [with Jessica] about what [financial] success has meant for me and most women of colour in comparison to our white counterparts.

''I told her about the gross disparity in our salaries. She provided a much-needed shoulder and listened. And then she did what she always does: She took up my cause and made it her own.

''As a friend, she's your biggest cheerleader; but as a colleague, she's your most vocal advocate.''

The 'Molly's Game' actress has even found herself helping to negotiate a better deal for an unnamed white male co-star.

She told the Hollywood Reporter: ''Someone will call my lawyer and say, 'I know Jessica's all for equal pay, so ...' And I've gotten a situation where I'm like, 'Sure, I'll tie my pay to him and bring his quote up.' ''