A group of 16 international law firms from the United States, Europe and Asia, including Latham & Watkins, Davis Polk & Wardwell and Clifford Chance, have joined forces as they seek to join a lawsuit in Hong Kong on behalf of a British lesbian in a landmark case that will decide whether spousal dependents in same-sex couples can obtain visas to reside with their partners in Hong Kong.

The law firms, along with 15 foreign banks and Amnesty International, are urging the Hong Kong Court of Final Appeal—Hong Kong’s highest court—to uphold a lower court’s decision to allow spousal dependent visas for same-sex couples.