American activist Lilly Ledbetter, whose lawsuit against her employer made her an icon in the equal pay movement, had died aged 86.
She died on Saturday night local time after a brief illness and surrounded by loved ones, according to a statement from her family.
Ms Ledbetter launched a lawsuit in the late 1990s when she discovered she was being paid less than her male co-workers for doing the same management job at a Goodyear tyre factory in Alabama.
Ms Ledbetter (left) continued to advocate for workplace equality throughout her life. (AP Photo: J. Scott Applewhite)
She received an anonymous note which brought the pay discrepancy to her attention after working at the company for almost two decades.
Ms Ledbetter initially won $US3.8 million ($5.6 million) in back pay and damages from a federal court.
But the Supreme Court ruled that she had filed her complaint too late and she never received the money.
Law named after Ledbetter
Ms Ledbetter's legal action gained national attention and led to then-president Barack Obama signing the Lilly Ledbetter Fair Pay Act in 2009.
The law gave workers the right to sue within 180 days of receiving each discriminatory pay cheque, aiming to remove the restrictions on fair-pay claims.
Ms Ledbetter said one of the achievements she was most proud of was that the Ledbetter act passed with bipartisan support.
Ms Ledbetter speaks at an event to advocate for the Paycheck Fairness Act in Washington, 2019. (AP Photo: J. Scott Applewhite)
National Women's Law Center chief program officer Emily Martin worked closely with Ledbetter.
Ms Martin said the law set an important precedent by making sure there was a way to "enforce the law" in equal pay disputes.
"She is really an inspiration in showing us how a loss does not mean you can't win," she said.
"We know her name because she lost … and she kept coming back from it and kept working until the day she died to change that loss into real gains for women across the country."
President Joe Biden marked the 15th anniversary of the Ledbetter's law earlier this year with new measures aimed at closing the gender pay gap.
This included a new rule which excluded the federal government from considering a person's current or past pay when determining their salary.
While Republicans have largely opposed the law, Ms Ledbetter continued to campaign to strengthen the Equal Pay Act of 1963 to protect workers from potential retaliation for discussing their pay
Praised for her legacy
Mr Obama praised Ms Ledbetter's legacy in a social media post and said he was "grateful for her advocacy and her friendship".
Equal Pay Today director and the national campaign director of Equal Rights Advocates, Deborah Vagins, said Ms Ledbetter lost her case and never saw a dime, but she was a "tireless advocate" for everyone.
"Every now and then, once in a generation, you meet these people who sacrifice everything for something even if it never benefits them," she said.
“She sparked a movement and changed the face of pay equity forever."
In a statement, Vice-President Kamala Harris promised to "continue to fight for the Paycheck Fairness Act to honour Lilly's legacy, and continue building a more fair and equitable future for women, and all Americans".
The team behind the film based on her life, LILLY, said portraying Ms Ledbetter was the privilege of a lifetime.
The film recently premiered at the Hamptons International Film Festival.
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Ms Ledbetter continued campaigning for equal pay policies throughout her life and was awarded the Future Is Female Lifetime Achievement Award last week.
She is survived by her two children, four grandchildren and three great-grandchildren.
AP/ABC