JK Rowling branded India Willoughby "a man" after the Supreme Court ruled that "sex", "man", and "woman" in the Equality Act must mean biological sex. The online spat began when India Willoughby, a transgender news reader, claimed that the judge who summarized the ruling is neighbors with JK Rowling. The author described India as "the gift that keeps on giving" and told her she "remains a man".

JK Rowling called for the entire NHS Fife health board to be sacked after it "vilified" a nurse who objected to a male doctor being allowed to use a changing room with her. She also demanded that Prime Minister Keir Starmer break his silence after the Supreme Court's ruling defined a woman based on biological sex. Rowling wants Starmer to express his views on the matter and referenced previous assertions that "trans women are women". The ruling may exclude trans women with gender recognition certificates from single-sex spaces if deemed "proportionate", potentially affecting access to bathrooms, sports, and workplaces.

J.K. Rowling caused a fresh storm online after openly ridiculing SNP MP Kirsty Blackman’s contribution to a Westminster Hall debate on the Equality Act in June 12, 2023. Highlighting Blackman’s comment — "I have an assumption that my chromosomes are probably XY but I don't know" — Rowling tweeted, "Footage like this must be preserved for posterity, or future generations will never believe how many idiots paraded their stupidity in the sincere belief that they were being clever." The scathing remark quickly went viral, reigniting fierce cultural battles and drawing sharp lines between Rowling’s supporters and her critics.