The law requires parole to be used only on a case-by-case basis, and only in the case of an urgent humanitarian need — such as a medical emergency and no time to get a visa — or a “significant” public benefit. That used to mean instances in which someone was needed to serve as a witness or assist in a criminal investigation.

Mr. Mayorkas upended that. He created categorical parole programs that welcomed tens of thousands of Afghans, hundreds of thousands of Ukrainians and millions more people from other countries.

Mr. Arthur calculated that nearly 3 million migrants were paroled into the U.S. during the Biden era. That accounts for a large portion, if not an outright majority, of the illegal immigrants who successfully settled in the U.S. under the previous administration.

The new consent decree likely would limit parole to “maybe a couple hundred a year,” he said.

In reaching the deal, Florida is harnessing a tactic called “sue and settle,” in which a plaintiff files a lawsuit against a friendly administration, and both sides agree to a new, binding policy that circumvents Congress and the usual administrative rulemaking process.

Left-leaning activists have been the most prolific with sue-and-settle deals, particularly in environmental and immigration matters. The Florida settlement suggests conservatives have figured out how to play as well.

Jennifer Coberly, a lawyer with the American Immigration Lawyers Association, said the deal appears to undermine the law.

“The biggest thing about this is it’s directly contrary to law,” she said. “Generally, [the law] does provide discretion to the administration, and this is saying you can’t do that for 15 years.”

Ms. Coberly said the agreement allows room for argument that some Biden parole programs would still be legal, such as the one that allowed Cubans, Haitians, Nicaraguans and Venezuelans to skip the southern border and fly directly into American airports without a visa.

Neither the Justice Department nor the Homeland Security Department responded to requests for comment for this report.

The key part of the decree reads: “Defendants agree not to issue any memorandum or otherwise adopt any policy that uses the Secretary of Homeland Security’s parole authority under Section 1182(d)(5) to create a categorical processing pathway for aliens at the border primarily to alleviate concerns over detention capacity or improve the Department of Homeland Security’s operational efficiency, including any memorandum or policy shifting the initiation of removal proceedings from the border to the interior or otherwise postponing the initiation of removal proceedings.”

The deal is binding on the federal government for 15 years.

Mr. Biden and Mr. Mayorkas turned to parole to try to alleviate pressure at the border. They didn’t want to maintain the stiff controls in place when President Trump left office, but the Homeland Security Department couldn’t handle the massive number of people who started streaming in.

Their answer was catch-and-release, and parole was the chief method.

Upon taking office, Mr. Trump’s administration quickly moved to suspend the Biden parole programs. It is now working to push out those who came through the legally questionable policies.

The consent decree grew out of a 2023 lawsuit filed by Florida Attorney General Ashley Moody and was finalized by her successor, Attorney General James Uthmeier.

“We thank the Trump administration for working with our office to obtain this result, which ensures that the next Democratic administration cannot abuse the parole system to allow another invasion of illegal aliens into our country,” Jae Williams, Mr. Uthmeier’s press secretary, told The Times.