In another sign that public opinion may be turning against the idea of medically transitioning minors to one sex from another, a group of Democratic state lawmakers in Texas has voted in favor of a bill to ban such treatment — the first Democrats to buck their party’s national leadership on the issue.

The Texas lawmakers — Harold Dutton of Houston, Tracy King of Batesville, Shawn Thierry of Houston, and Abel Herrero of Robstown — joined their Republican colleagues in the Texas house Monday and voted in favor of a measure already passed by the state senate. The vote was 87 to 56 and otherwise along party lines.

The bill would ban so-called gender-affirming care such as prescribing hormone treatment and puberty blocks for people under the age of 18. It would also ban transition-related surgeries on minors, and require those already receiving such treatments be “weaned off” them in a “medically appropriate” manner.

The latter is the only sticking point in the version of the bill previously passed by the state senate, which mandates an immediate cutoff of medical treatments. The senate will now have to decide whether to accept the house modifications and send the bill to Governor Abbott or work out the differences between the two measures in committee.

Mr. Abbott, who last year signed an executive order asking the state’s Department of Family and Protective Services to investigate parents who sign off on gender-affirming treatment for their children, is almost certain to sign the bill when it reaches his desk.

Texas would join more than a dozen other states that have passed similar legislation recently. Opponents of the Texas measure have staged raucous protests at the statehouse at Austin since it was introduced, disrupting the legislature’s proceedings at times and scuffling with security guards. Several had to be forcibly removed from the building during a protest earlier this month.

One of the Democratic representatives who voted in favor of the bill, Ms. Thierry, said in a public letter that she was voting in favor of the measure despite the threats she has received since staking out her position. The science on the safety of the procedures is far from settled, she said, and there is evidence “that these drugs can cause harm to a child’s health including early onset of osteoporosis, incontinence, increased risk of blood clotting, stroke and heart attack, infertility and sterility.”

In the letter, she lamented that debate surrounding the topic “has become polarized and politicized. In fact, while many of my constituents encouraged me to vote in favor of this legislation, hostile activists on social media platforms have made nasty political threats to influence my vote against this bill,” she wrote. “These personal, and even racist, attacks on me as an African American woman are neither productive nor persuasive.”

Ms. Thiery’s fellow Democrats in the state house had earlier attempted to torpedo the bill on procedural grounds, but ultimately failed. Opponents of the measure say it will deny critical medical care to teenagers at a critical point in their physical and emotional development. “The bill in front of us today is banning health care,” Democrat Mary González said on the House floor during debate. “Politics shouldn’t determine health care, period.”

Nationally, Democrats have marched in lockstep on the issue of medical treatment of minors who say they suffer from gender dysphoria. The Biden administration has repeatedly attacked what it calls the “dangerous anti-transgender legislative” movements across the country. “These bills are government overreach at its worst, they are un-American, and they must stop,” the president has said.