The actor's American Hustle co-star Jennifer Lawrence recently wrote an article about gender inequality in Lena Dunham's feminist blog, Lenny Letter, and admitted she was mad at herself for failing to fight for more money.

In the piece, titled Why Do I Make Less Than My Male Co-Stars?, Lawrence recalls finding out about the huge salary differences between her and co-stars like Cooper following the Sony Pictures hack attack last year (14), when producers' emails were leaked online.

She wrote, "When the Sony hack happened and I found out how much less I was being paid than the lucky people with d**ks, I didn't get mad at Sony. I got mad at myself. I failed as a negotiator because I gave up early. I didn't want to keep fighting over millions of dollars that, frankly, due to two franchises, I don't need."

Cooper's American Sniper and Burnt co-star, Sienna Miller, has also been vocal about the pay disparity between the sexes, revealing she walked away from a Broadway play after discovering she was to be paid less than half of what her male counterpart in the production was to receive.

Cooper recently applauded Miller for standing up for herself, and now he is encouraging film bosses to adopt a new way of doing business to make it fair for all involved.

He tells U.S. breakfast show Good Morning America, "You know, the idea of transparency is something that obviously would be beneficial. It's something you never talk about. You never hear about what somebody else is making when you're making a movie. Maybe it shouldn't be (hard to talk about), you know?

"In terms of today, it's so hard to get movies made, you're definitely... having (financial) conversations with your agent about 'take a cut' or 'do this' or 'put money over here', so why not say, 'OK, well, what's everybody making?' Let's make sure it's as equal as we can make it."

And he tells WENN, "I'm not aware of what anyone else gets unless you're approached to give some of your money; to make a movie is getting harder and harder and people are paying less and less and people are always taking pay cuts. That's my experience. So the only time you ever find out what anybody else makes is when you have to divvy up the pie so someone else can come on the movie.

"Why not just be transparent and say, 'Here's the pie. Let's divvy it up'."