HELENA — The 2025 Montana Legislature has passed a bill that aims to clearly define the sex of an individual as only male or female based on their biology. The bill comes after a Montana district court judge ruled a similar 2023 state law was unconstitutional.

Senate Bill 437, sponsored by Sen. Carl Grimm, R-Kila, passed third reading in the House 55 to 44 and will head to the governor’s desk.

Under the legislation, a person with XX chromosomes would be legally defined as female, and a person with XY chromosomes would be legally defined as male. The bill does allow for exceptions for individuals with congenital conditions.

The genders, as defined by the bill, would need to be used for government documents such as a person’s driver's license or birth certificate.

Supporters of SB 437 said it was needed to establish legal definitions, while opponents said it targets and stigmatizes transgender Montanans.

A similar law was passed in 2023, Senate Bill 458.

In February, the 2023 law was found unconstitutional by a state district court judge in Missoula. That case is currently under appeal.