Jennifer Lawrence has said she was made to stand in a nude line-up and told to lose weight by film producers at the start of her career.
Speaking at Elle's Women in Hollywood event, the 27-year-old said she felt she didn't have any power in the situation as an unknown actress.
She said she found that fame protected her from assault as her career went on.
"I will lend my voice to any boy, girl, man or woman who doesn't feel like they can protect themselves", she added.
The actress, who won an Oscar in 2013 for her role in Silver Linings Playbook, told the audience about auditioning for a film and being asked by a female producer to stand in a nude line-up.
She described the experience as "degrading and humiliating", as she was put next to girls she says were thinner than her.
"When I was much younger and starting out, I was told by producers of a film to lose 15 pounds in two weeks.
"One girl before me had already been fired for not losing the weight fast enough," she told an audience including Kristen Stewart, Margot Robbie and Ashley Greene.
"During this time a female producer had me do a nude line-up with about five women who were much, much, thinner than me. We all stood side by side with only tape on covering our privates."
Lawrence said the producer then told her she should "use the naked photos" of herself as "inspiration" for her diet.
She then went to complain to another producer about being called out over her weight.
"He said he didn't know why everyone thought I was so fat," Lawrence told the crowd, adding that he had commented that he thought she was attractive enough to sleep with.
The actress said she felt "trapped" by the experience and allowed the harassment to happen because she "didn't want to be a whistleblower" and thought it was what she had to do to further her career in Hollywood.
She told the audience: "In a dream world, everyone is treated with the exact same level of respect.
"But, until we reach that goal, I will lend my ear. I will lend my voice to any boy, girl, man, or woman who does not feel like they can protect themselves."
Lawrence's speech comes after the sexual harassment and assault accusations against film producer Harvey Weinstein, which has lead to a growing narrative on the mistreatment of women in the film industry and Hollywood in particular.
Lawrence worked with Weinstein on Silver Linings Playbook. She released a statement last week in response, which said: "This kind of abuse is inexcusable and absolutely upsetting.
"I worked with Harvey five years ago and I did not experience any form of harassment personally, nor did I know about any of these allegations."
Lawrence said in her speech it was time for people in Hollywood to "stop normalising these horrific situations."
On Tuesday, Weinstein resigned from the board of directors of his eponymous film production company.
He has been accused of rape, sexual assault and harassment, but has "unequivocally denied" any allegations of non-consensual sex.