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Fair Play for Women, a self-described "group of ordinary women" who say they are concerned their voices are not heard when it comes to transgender rights, have accused Twitter of making a "concerted attack on women's free speech."

In a letter to Martha Lane Fox, a member of Twitter's board of directors and a member of Britain's House of Lords, the U.K.-based group says that Twitter is deleting accounts or admonishing women for stating biological facts about men and women.

"Women are being told they have violated Twitter rules against hateful conduct by simply stating biological and legal facts," the group writes in its letter. "Women must not be shamed or silenced for speaking the reality."

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"This misogynistic, aggressive, violent movement, that has been embraced by the hard Left as the latest civil rights cause, has seen males colonize womanhood and hijack feminism for its own purposes."

— Fair Play for Women

Further in the letter, the women say they come from different walks of life (including mothers, members of the armed forces, unemployed and disabled) and are being admonished for saying "that males cannot become females," that "women do not have penises" and "that women’s spaces such as refuges should be safe havens for women only."

"This misogynistic, aggressive, violent movement, that has been embraced by the hard Left as the latest civil rights cause, has seen males colonize womanhood and hijack feminism for its own purposes," the women wrote in the letter.

The group cited several examples of women's accounts being compromised, including temporary limiting of certain features, for violating Twitter's rules against hateful conduct.

Interestingly enough, the group's Twitter account, @fairplaywomen, has not been suspended by Twitter.

"This is a concerted attack on women’s free speech," the women added in the letter. "The words we use to describe ourselves, our bodies, our biology and our experiences as women are becoming unsayable."

They request that Lane Fox, who has sat on Twitter's board of directors since April 2016, use her voice "to speak out against this new wave of misogyny and to stand up for women when we are being deprived of a platform from which to speak the truth."

The entire letter can be found here.

Twitter declined to comment, while Lane Fox, who tweeted earlier on Wednesday that she would be speaking at Google, has yet to respond to a request for comment from Fox News.

Fair Play for Women has also not responded to a request for comment.

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"According to the rules of Twitter, it is now ‘hateful conduct’ to call someone who is a man, a man."

— Trans activist Miranda Yardley

Trans activist Miranda Yardley said she was banned from Twitter for calling Green Party LGBT spokesperson Aimee Challenor, a trans woman, a man, the BBC reported.

"According to the rules of Twitter, it is now ‘hateful conduct’ to call someone who is a man, a man," Yardley wrote in a blog post. "The implication of this is that the concept of proscribed speech, things we are now not allowed to say, now extends to the truth. This is fundamentally illiberal."

A source familiar with Twitter's thinking said that the company enforces its rules when it finds content that violates the rules and that these particular accounts were not removed because of ideology.

Twitter has come under fire recently for purging groups of people who have violated its “hateful conduct policy."

In December 2017, Twitter began enforcing new rules to combat hateful and abusive content and a number of well-known far-right organizations and users were suspended.

The changes, which were announced in November 2017, broaden Twitter’s “hateful conduct policy” to permanently suspend any account — covering usernames, profile bios and display names — that displays “violent threats, multiple slurs, epithets, racist or sexist tropes, incites fear or reduces someone to less than human.”

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Among the accounts suspended in late 2017 are that of the founder of the white nationalist American Renaissance, Jared Taylor, the neo-Nazi Traditionalist Workers Party, Britain First’s main account and the accounts of its leaders Paul Golding and Jayda Fransen — whose anti-Muslim videos were retweeted by President Trump, for which the president later apologized.

Fox News' Christopher Carbone contributed to this story. Follow Chris Ciaccia on Twitter @Chris_Ciaccia