The Supreme Court of the United Kingdom unanimously ruled Wednesday that a woman is someone born biologically female, a move that now excludes transgender women from the legal definition of a woman.

Trans women can be excluded from some single-sex spaces and groups under the U.K. Equality Act, the five judges of the top court ruled. These spaces and groups include changing rooms, homeless shelters, swimming areas and medical or counseling services provided only to women.

The ruling means that even a transgender person with a certificate that recognizes them as female should not be considered a woman for equality purposes.

But Justice Patrick Hodge said its ruling "does not remove protection from trans people," who are "protected from discrimination on the ground of gender reassignment."

"Interpreting ‘sex’ as certificated sex would cut across the definitions of ‘man’ and ‘woman’ ... and, thus, the protected characteristic of sex in an incoherent way," Hodge said. "It would create heterogeneous groupings."

Women’s rights groups celebrated the ruling outside the court.

"Everyone knows what sex is and you can’t change it," said Susan Smith, co-director of For Women Scotland, which brought the case. "It’s common sense, basic common sense and the fact that we have been down a rabbit hole where people have tried to deny science and to deny reality and hopefully this will now see us back to, back to reality."

Hannah Ford, an employment lawyer, said that while the judgment will provide clarity on the controversial issue in the U.K., it would be a setback for transgender rights and there would be "an uphill battle" to ensure workplaces are welcoming places for trans people.