U.K. Prime Minister Rishi Sunak blocked a new Scottish law on gender change recognition, marking the first time in history the United Kingdom has wielded a 25-year-old statute to veto legislation in Scotland. The Scottish bill allows people aged 16 or older to self-declare their gender identity on legal documents, doing away with the need for a gender dysphoria diagnosis by a medical professional. Alister Jack, the British politician serving as Scottish secretary, said that Westminster had interceded over concerns that the law could impact equality laws across the U.K., but the argument has been dismissed by transgender rights groups—and stoked nationalist fervor in Scotland. Nicola Sturgeon, Scotland’s first minister, tweeted Monday that the move was “a full-frontal attack on our democratically elected Scottish Parliament and it’s ability to make it’s [sic] own decisions on devolved matters.” She added that the Scottish government intended to defend the legislation, possibly taking the case all the way to the U.K. Supreme Court.