A coalition of 19 Democrat-led states and the District of Columbia are suing the Department of Health and Human Services and Secretary Robert F. Kennedy Jr. over the administration’s latest effort to restrict gender transition treatments for minors.

The Oregon-led lawsuit, filed Tuesday, challenges Mr. Kennedy’s determination last week that treatments including puberty blockers, hormone therapy, and surgical procedures are ineffective and unsafe for children and adolescents experiencing gender dysphoria. His statement declared that such treatments “do not meet professionally recognized standards of health care” and warned that providers offering these services would be out of compliance with conditions for receiving Medicare and Medicaid reimbursements.

“Under my leadership, and answering President Trump’s call to action, the federal government will do everything in its power to stop unsafe, irreversible practices that put our children at risk,” Mr. Kennedy said. “This Administration will protect America’s most vulnerable. Our children deserve better — and we are delivering on that promise.”

The attorneys general of Oregon, New York, California, and other states behind the suit argue that the determination “exceeds the Secretary’s authority” and violates the Administrative Procedure Act and Medicare and Medicaid statutes, among other laws.

“Secretary Kennedy cannot unilaterally change medical standards by posting a document online, and no one should lose access to medically necessary health care because their federal government tried to interfere in decisions that belong in doctors’ offices,” New York’s attorney general, Letitia James said in a prepared statement.

The lawsuit marks the latest clash over President Trump’s broader push to curtail transgender procedures for minors. Eight days after his inauguration, Mr. Trump signed an executive order barring the federal government from funding or supporting what he called the “chemical and surgical mutilation” of children, describing it as a “dangerous trend” that will be a “stain on our Nation’s history.”

Mr. Kennedy’s December 18 determination draws from a department report issued earlier this year that recommended greater reliance on behavioral therapy over gender transition treatments for minors with gender dysphoria. The report also questioned whether youths under 18 are capable of consenting to life-altering treatments with irreversible consequences, including potential infertility.

Since the start of Mr. Trump’s second term, several major medical providers have scaled back gender transition treatments for children. Medicaid programs in fewer than half of the states currently cover such treatments, and at least 27 states have enacted laws restricting them.