Serena Williams and other prominent past and present American tennis players have expressed their support for a lawsuit filed by the US women’s national soccer team against their federation alleging gender discrimination in wages and conditions.

All 28 members of the US squad were named as plaintiffs in a federal court in Los Angeles on Friday, International Women’s Day.

Williams said pioneers in her sport had stood up for pay equality in the 1970s and it was the right time for soccer to level its playing field. “The pay discrepancy is ludicrous,” the 23-time grand slam singles champion told reporters after her second-round victory at the BNP Paribas Open in Indian Wells.

“It’s a battle, it’s a fight,” she said. “I think at some point, in every sport, you have to have those pioneers and maybe it’s time for soccer. I’m playing because someone else stood up and so what they are doing right now is hopefully for the future of women’s soccer.”

Billie Jean King also welcomed the lawsuit. “What better day than International Women’s Day for this lawsuit?” the 75-year-old former player, who won 12 grand slam singles titles, posted on Twitter.

“Sports are a microcosm of society. What is happening with the USWNT [United States women’s national soccer team] is happening in the workplace. The time has come to give these athletes what they deserve: equality.”

The work of King and her allies resulted in equal prize money for women and men at all four grand slams in 2007, when Wimbledon fell in line.

The issue still occasionally surfaces, however, and the Indian Wells tournament chief, Raymond Moore, quit under a cloud in 2016 after saying women’s tennis rode “on the coat-tails of the men”.

The former US Open champion Sloane Stephens also sent her encouragement to the soccer team on Friday. “I think there should be equal pay across the board for everyone, male or female,” the world number four said after her second-round loss at a tournament that has offered equal prize money to women and men since 2009. “But I’m happy for them. I hope they win.”

The lawsuit outlines years of alleged institutionalised gender discrimination, claiming travel conditions, medical personnel, promotion of games and training are less favourable for female players compared to the men.

The US Soccer Federation has yet to comment on the lawsuit.