Britain’s largest trade union, Unison, violated the law by permitting a transgender woman to stand for election to a senior female position within the organisation, according to a ruling issued by the trade unions regulator.

The dispute centers on Unison’s decision last May to allow a biological male, who identifies as a woman, to run for a seat on the union’s national executive committee (NEC) that was specifically reserved for women. The regulator found that by doing so, Unison contravened both its own internal rules and the Supreme Court’s interpretation of gender in this context.

Unison, which represents more than 1.3 million workers across the public sector in the United Kingdom, faced a formal complaint over this action. The complaint was upheld, marking a significant legal rebuke of the union’s approach to gender representation in leadership roles.

A spokesperson for the Trades Union Congress (TUC) acknowledged the ruling and indicated that the organisation will carefully consider its implications for its affiliated unions. The spokesperson said they would continue to engage with unions to address issues raised by the decision.

The ruling touches on broader debates within labour organisations and legal frameworks about gender identity policies and the eligibility requirements for roles designated for women. The case highlights ongoing tensions between inclusivity efforts and existing legal protections related to sex-based rights in employment and governance.