Several international bodies including the European Court of Human Rights, the World Professional Association for Transgender Health, and United Nations experts have said the requirement was discriminatory and infringed upon human rights.

However, some lawmakers and women’s rights groups in socially conservative Japan have said a ruling that challenges the law would sow confusion and undermine women’s rights. Japan’s Supreme Court threw out a similar legal case in 2019.

Human Rights Watch welcomed the ruling and said the government now had to follow up.

“The government is under the obligation to make any laws constitutional so the government now needs to act quickly to remove the clause,” said Kanae Doi, director for Japan of the rights group. “It’s late, but never too late.”

The case before the Court’s 15 justices was brought by a plaintiff who had been identified only as a transgender woman under the age of 50.

Reuters could not immediately reach the plaintiff’s lawyers for comment or confirm the judgment that was handed down in a closed court.

Japanese law states that people who want to change gender must present a diagnosis of gender dysphoria and meet five requirements.

Those requirements include being at least 18 years old; not being married; not having underage children; having genital organs that resemble those of the opposite gender; and having no reproductive glands or ones that have permanently lost their function.

The plaintiff’s lawyers said that the last two requirements violated their client’s constitutional right to pursue happiness and live without discrimination, and posed significant physical pain and financial burden to transgender people, media reported.

While many countries have moved to repeal laws requiring mandatory sterilisation to legally change gender, transgender rights remain controversial in Japan.

A petition organised by seven groups that support the surgery requirement collected more than 20,000 signatures as of yesterday.

Protect the Definition of Women, a group that supports upholding the surgery requirement, submitted a separate petition to the Supreme Court last week, saying dropping the requirement would “significantly violate women’s rights and dignity”.

Last month, a group of lawmakers from the ruling Liberal Democratic Party issued a statement saying any ruling that deemed the law unconstitutional would sow confusion.