Planting its flag firmly on the more progressive edges of the Democratic movement, the Biden administration has signaled to state legislators that it will not stand idly by while they seek to pass laws that affect transgender Americans and their allies in the medical and educational establishments.

In a letter sent last week to state attorneys general across the nation, a Justice Department official said recent efforts by state legislators to prevent underage youth from seeking access to “gender-affirming care” may run afoul of several federal civil rights laws.

The assistant attorney general who signed the letter, Kristen Clark of the Civil Rights Division, said that “intentionally erecting discriminatory barriers to prevent individuals from receiving gender-affirming care” is unlawful and could jeapordize the federal funding of any institution that enacts those barriers.

“The Department and the federal government more generally have a strong interest in protecting the constitutional rights of individuals who are lesbian, gay, bisexual, transgender, queer, intersex, nonbinary, or otherwise gender-nonconforming, and in ensuring compliance with federal civil rights statutes,” Ms. Clark warned.

“Gender-affirming care” is the currently preferred language in progressive circles for what used to be referred to as sex-change therapy. Such treatment can range from puberty blockers and hormone therapy to surgeries that physically alter minors to conform with their preferred gender identity.

Ms. Clark’s letter was in response to a wave of legislation at the state level aiming to, among other things, restrict treatment for minors seeking therapy for gender dysphoria, a condition in which patients suffer from psychological distress because their gender identity is different from their sex at birth.

Some studies have suggested that gender dysphoria can manifest itself in children as young as 7 years old, and can, if untreated, lead to a number of mental health disorders such as anxiety, depression, substance abuse, and suicidal thoughts. 

Last month, Texas was the latest state to wade into the politically charged debate over such treatments when its Republican governor, Greg Abbott, suggested in a letter to state agencies that some of the methods used to treat gender dysphoria could constitute child abuse under Texas state law. 

Mr. Abbott said medical professionals who perform elective procedures for gender transitioning — among them reassignment surgeries, mastectomies, the removal of certain body parts, and the administration of puberty-blocking drugs or hormones such as testosterone or estrogen — on minors may be opening themselves up to criminal charges.

At least 15 states have passed legislation in the past two years that is more or less in line with Mr. Abbott’s opinions on the topic. Many of the laws seek to punish health care providers for administering such care. Six of the states penalize parents for seeking out such care for their children, according to the Williams Institute at the UCLA School of Law.

The Biden administration’s assertion that “early gender-affirming care is crucial to [the] overall health and well-being” of transgender individuals is not universally accepted as gospel. Even some proponents of such treatment have begun to question the conventional wisdom that puberty blockers and hormone treatments are fully reversible and harmless.

Erica Anderson, a clinical psychologist at the University of California San Francisco’s Child and Adolescent Gender Clinic who is herself a transgender woman, told the author Abigail Shrier — whose book, “Irreversible Damage: The Transgender Craze Seducing Our Daughters,” caused an uproar when it was published in 2020 — that “sloppy” health care work is increasing the likelihood that some patients, or their parents, may come to regret transitioning at an early age.

“That is going to earn me a lot of criticism from some colleagues, but given what I see — and I’m sorry, but it’s my actual experience as a psychologist treating gender variant youth — I’m worried that decisions will be made that will later be regretted by those making them,” Ms. Anderson said.

While most medical guidelines advise against permanent treatments such as surgery before the age of 18, the number of adult Americans seeking to physically alter themselves because of changes to their sexual identity has skyrocketed in the last several years, according the American Academy of Plastic Surgeons.

There were 2,740 “gender confirmation” surgeries performed in the United States in 2015, according to the academy, 1,380 of them male-to-female and 1,360 of them female-to-male. In 2020, there were 16,353 such surgeries, the majority of them involving alterations to the breast or chest of the patients.

Republicans on the campaign circuit have taken note of the Biden administration’s unequivocal language on the topic of transgender rights and are staking their own claims on the opposite side of the debate. Some see the issue as a natural extension of the fracas over critical race and gender theories in public schools that has riled up conservatives in recent months and helped put a Republican governor into office in Virginia late last year.

During a rally at Michigan last weekend, President Trump ridiculed the Biden administration for supporting the rights of biological males who identify as female to compete against women in collegiate sports. 

“With their extremist sex and gender ideology, the Democrat Party is waging war on reality, war on science, war on children, war on women,” Mr. Trump said.