The US Supreme Court on Monday upheld a policy in Oregon public schools that allowed transgender students to use the bathrooms and locker rooms matching their gender identity.
The nation's highest court, which has six conservative justices out of nine, did not explain why it declined to hear the arguments of the parents contesting the policy, particularly on the grounds of religious arguments or the right to privacy.
The decision is the latest episode in the "toilet wars" saga that has raged for several years in the US.
Democratic president Barack Obama's administration issued landmark guidance in 2016 requiring public schools to let students use the bathrooms and locker rooms matching the gender with which they identify, rather than the one on their birth certificate.
President Donald Trump's administration overturned those rules in February 2018, leaving the decision to local jurisdictions.
Some conservative states passed laws forcing students to use the bathrooms corresponding with their birth sex. But others adopted the previous administration's stance, including the Dallas school district in the state of Oregon.
The Supreme Court's decision to leave the policy in place was welcomed by advocates for sexual minorities, including the powerful American Civil Liberties Union (ACLU).
"The Supreme Court has once again said that transgender youth are not a threat to other students," said Chase Strangio, the ACLU's deputy director for trans justice.
The court has sent "an important and powerful message" to transgender people at a moment where several state are preparing new legislative offensives against them, Strangio added in a statement.