The Harry Potter author claimed the party could “no longer be counted on to defend women’s rights” in a series of tweets rebuffing the politician.
She also claimed Sir Keir “publicly misrepresented” the 2010 Equality Act which legally protects people from discrimination in the workplace and in wider society.
In her posts, the 56-year-old writer said women’s anger was “growing” on the topic.
Her criticism came after the opposition leader said: “A woman is a female adult and, in addition to that, trans women are women, and that is not just my view — that is actually the law.”
But the author hit back writing: “I don’t think our politicians have the slightest idea how much anger is building among women from all walks of life at the attempts to threaten and intimidate them out of speaking publicly about their own rights, their own bodies and their own lives.
“Among the thousands of letters and emails I’ve received are disillusioned members of Labour, the Greens, the Lib Dems and the SNP. Women are scared, outraged and angry at the deaf ear turned to their well-founded concerns. But women are organising.
“Now Keir Starmer publicly misrepresents equalities law, in yet another indication that the Labour Party can no longer be counted on to defend women’s rights. But I repeat: women are organising across party lines, and their resolve and their anger are growing.”
Rowling has claimed she has received many messages from women agreeing with her view and she said lesbians are also coming under attack for “not wishing to be redefined”.
She added: “Innumerable gay people have been in touch with me to say exactly this. Like women, they – especially lesbians – are under attack for not wishing to be redefined and for refusing to use ideological language they find offensive.”
Sir Keir has called for changes to the Gender Recognition Act to enable legal recognition of their gender based on self-declaration, without needing a medical diagnosis.
He told The Times: “The process that people have to go through does need to be looked at. If you talk to anybody who’s been through the process there’s a real issue about respect and dignity.”
The Labour leader also supports one of the key demands of feminists who have clashed with transgender activists by insisting on safe spaces, such as toilets, for those born as women.
He said: “I believe in safe spaces for women, I’m very clear about those too. I think the 2010 act, the Equality Act, which does provide for safe spaces for women is right. And therefore I’m very straightforward about this.”