A pro-female athletes organization announced that women in Britain are dropping out of recreational sports because they were forced to compete against biological males who consider themselves “transgender women.”

Fair Play for Women, a group fighting to prevent female athletes from having to compete against men who identify as women, claims that trans competition has already forced many women to quit athletics altogether.

The U.K.-based Fair Play for Women is speaking out about it, according to a report in the Daily Mail, which said the growing controversy over transgender women competing against women in elite sports is trickling down to amateur sports:

Fiona McAnena, director of sport campaigns at FPFW, which has lobbied to keep women’s sports single- sex, warned: ‘If you think this is a very small problem, think again.’

“This issue is hitting women’s sport right across the UK, and sadly it is pushing some women to completely drop out,” McAnena said.

“Especially for teenage girls, just knowing that there is a trans woman at their club can be enough to put them off going for fear of an embarrassing encounter in the changing room or toilet,” she added.

A dossier compiled by FPFW includes testimony from a female hockey player in an amateur London league who walked off the pitch when given the task of marking a transgender opponent.

“The person was 6ft 4in and had an Adam’s apple,’ the woman said. ‘Every time I was going for the ball, the transgender woman was far faster, and after a few minutes, I just took myself off.

“I was in tears,” the hockey player said. “I came to play against a female opposition, and there was a male on the pitch. I just felt the sense of fairness was not there.”

A parent and cricket coach from the South of England told FPFW he was concerned about the safety of girls, one as young as 12, asked to play against a team containing a trans woman.

“As father to these girls (aged 14 and 16), I find that unacceptable, uncomfortable and dangerous, both morally and physically,’ the father and coach said.

The Mail cited the remarks of cyclist Bo Novak, who said she stopped taking part in the women-only road cycling trips when a transgender woman joined.

“It was advertised as leisure rides for women in small groups led by a woman,” Novak said. “But a male-bodied person was leading the group, not just taking part. He was much stronger than the rest of us and went too fast.”

The woman complained, but after her concerns were ignored, she dropped out, according to the Mail.

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