Montana health officials adopted a rule on Friday that permanently prohibits people from changing the gender on their birth certificates.
Before the new rule, transgender people wishing to alter their birth certificate had only been required to provide an affidavit to the state health department.
Now, the Montana Department of Public Health and Human Services will no longer record the "gender" section on birth certificates and will replace it with a "sex" category that only offers options for male or female. The "sex" listing can only be changed in rare circumstances.
The rule states that sex is "immutable" and gender was described as a "social construct" that can change over time.
It also says the sex listed on a person's birth certificate can only be changed if their sex is misidentified when they are born or if the sex was wrongly recorded because of "a scrivener’s error."
The new rule comes just ahead of court arguments regarding a similar rule that has been in effect on an emergency basis since May.
Judge Michael Moses had temporarily blocked a 2021 state law that made it difficult for transgender people to alter their birth certificates. The law stated that people had to have a "surgical procedure" prior to changing the sex on their birth certificate. Republican Gov. Greg Gianforte's administration then blocked post-surgery changes to birth certificates.
Transgender plaintiffs represented by the American Civil Liberties Union of Montana have argued that blocking them from changing their birth certificates puts them at risk of embarrassment, discrimination, harassment or violence if they are asked to provide the document.
ACLU attorney Akilah Lane said the new rule was "further evidence of the state's non-compliance" with Moses' order from April.
And Democratic state lawmakers have slammed the Greg Gianforte administration for the new rule that they view as an attempt to get around Moses' order. The lawmakers have called the health department rule a "blatant abuse of power" intended to undermine the courts.
The Associated Press contributed to this report.