Reese Witherspoon and Natalie Portman are among hundreds of prominent Hollywood women who have launched a new initiative to fight sexual harassment.
Kerry Washington, Eva Longoria, Ashley Judd and Meryl Streep are also backing Time's Up, which was created in the wake of the sexual assault and harassment allegations which have emerged in recent months.
The campaign includes a legal fund to help women protect themselves from sexual misconduct.
The group unveiled its mission with a full page advert in The New York Times and has launched a website.
The letter said: "We particularly want to lift up the voices, power and strength of women working in low-wage industries where the lack of financial stability makes them vulnerable to high rates of gender-based violence and exploitation."
Time's Up will advocate for legislation to tackle workplace harassment.
"The struggle for women to break in, to rise up the ranks and to simply be heard and acknowledged in male-dominated workplaces must end; time's up on this impenetrable monopoly," said the letter.
The group is also is backing the movement for women to wear black, in solidarity with those who have been sexually harassed, at the Golden Globes.