The 1975 will no longer play festivals that have too few female artists on the bill, singer Matty Healy has pledged.
The musician made the promise after this year's Reading and Leeds festivals were criticised for a gender imbalance.
Only 20 of the 91 acts on the initial line-up are women, leading a journalist to challenge Healy to insist on greater equality at festivals where he plays.
"Take this as me signing this contract," said the singer, whose band headlined Reading and Leeds in 2019.
The 1975 won best British group and best British album at last year's Brit Awards.
'Act not chat'
Guardian writer Laura Snapes asked the frontman to "only play festivals that commit to X% (ideally 50%!) acts that include women and non binary performers".
Healy accepted the challenge, saying "people need to act, not chat".
He wrote on Twitter: "I have agreed to some festivals already that may not adhere to this [condition] and I would never let fans down who already have tickets.
"But from now I will and believe this is how male artist can be true allies."
Take this as me signing this contract - I have agreed to some festivals already that may not adhere to this and I would never let fans down who already have tickets. But from now I will and believe this is how male artist can be true allies ❤️ https://t.co/1eaZG2hEze— 🥾🌍 (@Truman_Black) February 12, 2020
He didn't specify what proportion of female acts he would insist on, and added that his agents would be "having kittens" about his apparently impromptu pledge.
But he insisted "time's up" for any festival that doesn't support women.
"The point is that Reading and Leeds with more women would be honestly the best festival in the world," he concluded.
"Let's not judge people and give the benefit of the doubt that people are going to start to listening. I can feel the change!"
The 1975 are holding their own one-day festival in London's Finsbury Park this summer, where six of the seven support acts are female.
The issue of gender balance on festival line-ups has been a talking point since 2015, when the music blog Crack in the Road tweeted a doctored image of the Reading and Leeds poster, erasing all acts that didn't include a female performer. Only 10 groups remained.
Writer and promoter Lucy McCourt has continued the tradition, producing redacted posters for the 2020 festival season and exposing the industry's lack of progress.
Analysis by the BBC suggests only 8% of this year's major festival headliners are female, with just three acts - Taylor Swift, Little Mix and Haim - topping the bill at the UK's 16 biggest festivals.
Some progress has been made in the past five years - with more than 300 festivals and music organisations signing up to the Keychange initiative, which aims to achieve a 50/50 gender balance by 2022.
Maxie Gedge, who runs Keychange at the PRS Foundation, welcomed Healy's statement, calling him "an ally that we appreciate".
"Working together and doing everything we can to ensure equality in the music industry is crucial if we're to make change happen.
"Since 2017 over 300 festivals and music organisations have signed up to our Keychange pledge for gender equality and we'd be more than happy to put Matt in touch with all of the festivals that pledged - including those that have already reached a gender parity with their line-ups ahead of their 2022 target date."
Geoff Ellis, who organises Scotland's TRNSMT festival, caused outrage earlier this year when he suggested it would take "several years" for equality to be achieved.
"There's far, far less female artists," he told the BBC. "We need to get more females picking up guitars, forming bands, playing in bands."
While there is some truth to his comments - only 20% of artists signed to a UK record label are female - other festivals have shown that gender balance is possible.
In 2019, Spain's Primavera festival had a 50/50 line-up, while Latitude managed a 40/60 split between women and men. Meanwhile, 59% of the acts who played at Liverpool Sound City last summer were female or female-fronted.
The BBC 6 Music Festival, which takes place in Camden next month, will host an all-female concert at the Roundhouse to celebrate International Women's Day. Across all the days and stages, the line-up is 45% female, 39% male and 16% mixed.
Healy said he wanted to see other male musicians taking a pledge to ensure equal representation, telling The Guardian: "It's something that, if everyone gets on board, we can fix."
He said he was "sceptical" that festivals would jeopardise their "short-term or long-term personal profit" to make a change, but added: "We should accept that some people are willing to learn."