U.K.-based organizations Girlguiding and the National Federation of Women’s Institutes announced this week that they will ban trans women and girls from joining.

The change comes eight months after the U.K. Supreme Court ruled that the legal definition of a woman or a girl is based on one’s sex at birth under equality law.

First formed in 1910, Girlguiding is the largest youth organization for young girls in the U.K., and is the original Girl Guides organization in the world. Girlguiding said in a statement that the “difficult decision” was made after receiving expert legal advice—as well as input from its members and board of trustees.

The NFWI also announced that it would no longer offer formal memberships to trans women. Starting in April 2026, new and renewing members will be expected to confirm their sex at birth to join.

NFWI CEO Melissa Green said the decision was made with the “utmost regret and sadness” and that the Supreme Court ruling gave them “no choice” but to exclude trans women from its membership.

Back in 2023, Green said the Women’s Institute would continue to “celebrate” its trans members after an internal group tried to overturn its inclusivity policy. The policy allowed trans women to join the organization and was in effect since the 1970s before becoming official in 2015.

In the announcement, Green highlighted her frustration with the ripple effects of the Supreme Court ruling, saying: “It remains our firm belief that transgender women are women, and that doesn’t change.”