Thousands of trans rights protesters gathered in central London, days after the U.K.‘s Supreme Court ruled that a woman is someone born biologically female and that transgender women are excluded from that legal definition.

The United Kingdom’s highest court ruled that the legal definition of “woman” excludes trans women, in a case with sweeping consequences for how equality laws are applied.

Anti-trans advocacy group For Women Scotland, which counts author J.K. Rowling as a supporter, challenged a Scottish law, which led to the ruling.