What to know about Montana’s new sex definition bill

Nearly a year after it passed the Legislature, Gov. Greg Gianforte signed a bill Tuesday defining sex as binary, based on a person’s reproductive system. The move officially amends wide ranging sections of Montana law to include new definitions of “male,” “female,” “sex,” and “gender.”

Senate Bill 437 is largely similar to a 2023 law that was declared unconstitutional twice — first in June 2024, because its subject wasn’t clear in its title, and second in February 2025 because a judge found it violated the equal protections clause of the Montana Constitution.

So, how is this new law different? What does it mean for Montanans? Why did it take so long to be signed? Let’s break it down.

What does Senate Bill 437 say?

The bill defines sex as whether someone is male or female, as distinguished by their reproductive system. Specifically, the legislation defines those categories based on a person’s “primary sexual anatomy.”

It defines a female as an individual who “naturally has, had, will have or would have but for a congenital anomaly or intentional or unintentional disruption” a reproductive system that uses the ova ( or egg cell ) for fertilization. In the same way, the law defines a male as someone with a reproductive system that uses sperm for fertilization.

While the definitions are largely similar to the 2023 bill, SB 437 removes references to sex markers in a person’s chromosomes.

It also adds definitions of man, woman, father and mother based on the definitions of male and female.

The bill states that the term “gender” must be considered a synonym for sex — as defined in the new legislation — and may not be considered synonymous with a person’s gender identity, experienced gender, gender expression or gender role. The term “gender identity,” if used in state law or rules, may not be considered a substitute for sex or gender.

In essence, supporters of the new law say they want categories of male and female to be cemented and consistent — not evolving or subjective based on how a person identifies.

These new definitions apply anywhere in Montana law that mentions the words sex, gender, male, female, man, woman, father or mother — more than 60 sections governing a wide range of topics.

What concretely does it change and for whom?

The bill’s wide reach changes laws that govern driver’s licenses, marriage licenses and the state’s anti-discrimination protections, which apply, among other arenas, to workforce and labor disputes. It also touches less obvious laws, including those that govern the representation of men and women on certain state boards and commissions and local precinct committees.

Missoula Democrat Rep. Zooey Zephyr, a transgender woman, told MTFP Friday the law discriminates against every aspect of trans peoples’ lives. It also erases intersex, nonbinary and Two Spirit people “from cradle to grave,” she said.

Plaintiffs in the lawsuit challenging the similar law passed in 2023 argued the legislation deprived them and other Montanans of legal recognition and protection from discrimination. Among other examples, plaintiffs said they would be put at risk every time they had to produce a drivers license where the listed sex did not match their appearance — whether applying for housing or being carded at a bar. Zephyr said the 2025 bill is “essentially the same.”

Residents applying for driver’s licenses or marriage licenses are now required to include their sex as defined by the new state law. For people who do not identify with their sex assigned at birth, opponents have argued the legislation would require Montanans to misgender themselves or disclose private information.

Changing identity documents to align with a person’s gender identity used to be easier in Montana under the administration of former Democratic Gov. Steve Bullock. But many of those policies have shifted since the governor’s office changed parties in 2021. In recent years, there have been multiple Montana court cases related to how the state treats sex designations in identity documents — such as drivers licenses. Another recent case has challenged a law restricting transgender residents’ access to public bathrooms and locker rooms.

Who supports and opposes it?

The bill passed the Montana Senate and House in April of last year largely on party lines, with almost all Republicans in support and all Democrats opposed.

While introducing the bill on the Senate floor last March, Sen. Carl Glimm, R-Kila, the bill’s sponsor, said the definitions are similar to those President Donald Trump proposed at the federal level. In February 2025, the U.S. Department of Health and Human Services issued guidance defining sex as binary and defining male and female based on reproductive systems.

Glimm told MTFP the bill is a “commonsense” measure that Montanans support because it has become necessary to have a definition for male and female in state law.

“In our culture, it’s gotten to where that is not clear,” he said. “It becomes a fuzzy line for some, so we just need to have clear definitions in law so that it’s clear what we’re talking about when we talk about a male or female.”

Other supporters of the bill included the conservative advocacy organization Montana Family Foundation, whose representative Derek Oestreicher said the definitions were needed to ensure consistency across legal and medical documents and government records.

Opponents said the bill is unnecessary, discriminates against transgender, nonbinary, intersex and other gender non-confirming people and requires people to misgender themselves or risk penalties.

Zephyr told MTFP the bill will contribute to a systemic erasure of trans, nonbinary, intersex and Two-Spirit people from public life.

“The Republicans design bills like this to do two things,” Zephyr said. “Make life hard for trans people in their continued crusade to make it hard to exist as an LGBTQ person in the state of Montana.” The other impact, Zephyr continued, “is to bring up the boogeyman of trans people as a distraction to the growing resentment of Republican policies in this state and this country.”

Zephyr said Montana Republicans’ fixation on regulating trans people echoes the actions of far-right Republicans in Congress and President Trump. One example, Zephyr said, is Trump’s recent request to add restrictions on transgender athletes and a ban on gender-affirming surgical care for minors to the SAVE America Act, legislation that would increase documents required for voter registration.

Is it likely to stick?

Both Glimm and Zephyr said they expect the bill to be challenged in court.

The Helena-based nonprofit Upper Seven Law, which represented plaintiffs suing the state over the 2023 version of the sex definition law, notified a Missoula state District Court this week that it will seek permission to file a supplemental complaint to include the new law, said Rylee Sommers-Flanagan, the firm’s executive director. That request, along with the complaint, will be filed on or before April 6, she said.

If the judge allows the complaint to move forward, Upper Seven will request a preliminary injunction or temporary restraining order to halt SB 437 during litigation, Sommers-Flanagan said. If the judge does not allow the supplemental complaint, Upper Seven plans to immediately file a new complaint against SB 437 in district court, she said.

“This is a second attempt at almost exactly the same thing Montana courts already determined violates the state constitution,” Sommers-Flanagan said. “It’s a disappointing use of state resources.”

The Legislature isn’t in session. Why wasn’t the bill signed until this month?

SB 437 was technically passed by both chambers of the Legislature in mid-April, 2025. But the bill’s progress was then stalled by procedural hurdles — apparently by political design — that blocked its path to the governor’s desk.

Every bill passed by lawmakers must be signed by the president of the Senate and the speaker of the House before being transmitted to the governor. The bill’s legislative paper trail shows that it was signed by Senate President Matt Regier within a few days of clearing its final vote. But then, according to the legislative record, the bill sat, and kept sitting, on House Speaker Brandon Ler’s desk.

In August, nearly four months after the bill passed its final chamber, a spokesperson for House Republicans said the ongoing cooling period was intentional.

“Leadership has chosen to hold the bill to prevent it from being immediately tied up with ongoing litigation over a similar measure passed last session,” spokesperson Joey Grewell said in a then-press release. He added that SB 437 would “ultimately be signed into law,” but did not forecast a specific date.

The legislative record shows that Ler signed SB 437 on March 24, 2026. It was transmitted to Gianforte’s office and signed by the governor the same day.

Todd Everts, the director of legal services for the Legislature, told MTFP in an email this week that the Legislature’s joint rules only describe the steps a bill “may” take after passing both chambers. In the email, Everts highlighted the word “may” in bright yellow.

The rule determining when a bill proceeds to the governor’s desk, Everts said, “is discretionary.”

What happens next?

Sommers-Flanagan said there may be a fight over the request to add SB 437 to an existing lawsuit. If the complaint moves forward, Sommers-Flanagan said she expects the case could advance relatively quickly. She said adding the complaint to the active case is more efficient, though Upper Seven would have been prepared to challenge SB 437 regardless.

Glimm said right now the law is passed and in effect, so he shouldn’t have to bring a similar bill next session. However, “the courts are not staying in their lane on this issue,” he said.

Zephyr said the 2027 session will depend on the makeup of the Legislature following this year’s election. This fall, 125 legislative seats are up for election.

“If Montana echoes the rest of the country, we’ve seen a pretty deep exhaustion with Republican policies. Hopefully the 2027 Legislature will be the year that the MAGA faction of the Republicans finally stop trying to use LGBTQ people as a boogeyman and actually take governing seriously,” she said.

Mara Silvers contributed reporting.

This story was originally published by Montana Free Press and distributed through a partnership with The Associated Press.