CONCORD, N.H. — When lawmakers reported to the New Hampshire State House on Thursday morning, those who hoped to freshen up before the legislative session began were met with an unusual sight at the restroom doors: guards standing sentry.

These guards weren’t there on official business. They had no authority, and they didn’t block anyone from entering. But each self-appointed bathroom bouncer wore a paper badge that said “genital observation police” — a cheeky way of expressing opposition to legislation they said would undermine privacy and invite discrimination against transgender, intersex, and gender-nonconforming people.

“Sometimes we are serious and we try to talk to our legislators,” said Nancy Brennan, as she stood guard outside the second-floor men’s room. “And sometimes we find a little bit of snark and humor can get the attention.”

To drive their point home, the protestors distributed small cards telling people they would need to allow a GOP lawmaker to inspect their private parts before they could use the restrooms, which are located just a few steps from each legislative chamber. Some passersby scoffed at the demonstration as immature, while others chuckled.

Brennan, who is affiliated with the Kent Street Coalition, a progressive political advocacy group in New Hampshire, said she came up with the badge idea to criticize both House Bill 148 — a Republican-backed bill that would add exceptions to the gender identity protections that currently exist in New Hampshire law — and those who support such legislation.

“A lot of these legislators are using this for points,” she said. “They don’t want to talk transgender people. They don’t want to understand where they’re coming from. They demonize them. And they demonize those of us who support them.”

While opponents of HB 148 say it will place transgender people and others at risk, proponents say they aim to protect women and girls. The legislation would identify certain situations as appropriate for classifying people on the basis of biological sex, rather than gender identity. Those situations include jails and other detention facilities; athletic or sporting events in which males are generally recognized as enjoying a physical advantage; locker rooms and multi-person bathrooms.

The legislation would allow, but not require, public and private entities statewide to separate such facilities and events by sex rather than gender.

Kamren Munz, a trans nonbinary person who has been using the men’s room for the past five years, said they have faced restroom-related discrimination, including being told to leave a facility based on perceptions of their gender, and HB 148 would make matters worse.

“It’s encouraging the general public to basically ask very invasive questions,” they said.

Munz — a former public school teacher who left the profession after drawing scrutiny from New Hampshire’s socially conservative education commissioner — was among the protesters who gathered Thursday morning at the urging of 603 Equality, an LGBTQ+ advocacy group. While Munz stood outside the second-floor women’s room, fellow demonstrators lined the halls and sang about their opposition to the legislation.

Despite the protest, HB 148 was approved in a party-line vote later Thursday by the Republicans who hold a supermajority in the 24-member New Hampshire Senate. The measure had already passed the 400-member House in March with approval from 198 Republicans, two Democrats, and one independent.

During debate, Republican Senator William M. Gannon said his support for the legislation was based partly on his daughter’s experience competing on an athletic field against a transgender opponent who was much taller and stronger than her. Gannon also said single-sex detention facilities are important for the safety of those detained.

Republican Senator Regina M. Birdsell said lawmakers need to protect privacy and the fairness of athletic competition for women and girls, who face blowback if they speak out about their discomfort when transgender people are allowed in single-sex spaces.

“Women are being marginalized in this environment,” she said, “and as far as I’m concerned, this has to stop.”

In a social media post, Republican Representative Lisa Mazur of said the badge-wearing protesters were “fighting against everything women have fought so hard for over the years.”

This legislation is very similar to a bill that Republican former governor Christopher T. Sununu vetoed last year, when he signed into law a separate bill that bars transgender girls from girls’ school sports. (The constitutionality of that sports law is being disputed in a pending federal lawsuit.)

Sununu had signed legislation in 2018 and 2019 to add gender identity to the state’s nondiscrimination law and apply those protections to school settings. He said some of the carve-outs that lawmakers wanted to add in 2024 tried “to solve problems that have not presented themselves in New Hampshire.” The legislation would invite “unnecessary discord,” he said.

It’s not yet clear whether Republican Governor Kelly A. Ayotte, who took office in January, will sign HB 148 into law.

Steven Porter can be reached at steven.porter@globe.com. Follow him @reporterporter.