The U.K. Supreme Court has ruled the country's 2010 Equality Act defines a woman as someone born biologically female in a potential landmark case for transgender rights.

The ruling was a blow to trans rights advocates and cheered by For Women Scotland, which filed the case. The government said it “brings clarity and confidence.”

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.