Florida Gov. Ron DeSantis is vowing to fight back against what he says is the Biden administration's unlawful use of parole authority to allow illegal migrants to fly into the U.S. in the tens of thousands each month as a new report finds Miami is a top destination for migrants on those flights.

"It’s an illegal program. They’re bringing people in who don’t have a right to be in this country from foreign countries," DeSantis said on Wednesday.

His administration highlighted a study by the Center for Immigration Studies, which, using Customs and Border Protection (CBP) data, reported that migrants admitted to the U.S. via the parole program for Cubans, Haitians, Nicaraguans and Venezuelans (CHNV) were overwhelmingly flying to Miami. The study found that more than 326,000 migrants have arrived so far via Miami.

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"This is but one of the many examples of how Biden’s egregious and unlawful immigration policies are disproportionately taxing the resources of certain states," Florida Attorney General Ashley Moody said in a statement on Tuesday. "As with Biden’s other unlawful policies, we will continue to fight the CHNV program in court."

The policy was first announced for Venezuelans in October 2022, which allowed a limited number to fly or travel directly into the U.S. as long as they had not entered illegally, had a sponsor in the U.S. already, and passed certain biometric and biographical vetting. The program does not itself facilitate flights, and migrants are responsible for their own travel.

In January 2023, the administration announced that the program was expanding to include Haitians, Nicaraguans and Cubans and that the program would allow up to 30,000 people per month into the U.S. It allows for migrants to receive work permits and a two-year authorization to live in the U.S. and was announced alongside an expansion of Title 42 expulsions to include those nationalities. By the end of February 2024, more than 386,000 nationals have arrived under the parole program, DHS said.

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It has formed part of the administration’s strategy to expand "lawful pathways" for migration amid its broader efforts to slow illegal crossings at the southern border amid a record surge.

The program’s announcement was met by a lawsuit by 20 states, which argued that it is in excess of the limited power for use of parole, which is allowed by Congress only on a "case-by-case basis for urgent humanitarian reasons or significant public benefit." The states argued that it "amounts to the creation of a new visa program that allows hundreds of thousands of aliens to enter the United States who otherwise have no basis for doing so."

"The federal government is encouraging illegal immigration and even aiding these individuals to enter the country," DeSantis communications director Bryan Griffin said. "They’ve cloaked these secretive flights as a lawful parole program."

That lawsuit was recently struck down by a U.S. district judge, but the states have appealed. Department of Homeland Security (DHS) Secretary Alejandro Mayorkas defended the program, saying the processes are a "safe and orderly way to reach the United States" and have led to a reduction in numbers of those nationalities.

"It is a key element of our efforts to address the unprecedented level of migration throughout our hemisphere, and other countries around the world see it as a model to tackle the challenge of increased irregular migration that they too are experiencing," Mayorkas said.

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"More than 14 months ago, on January 5, 2023, DHS announced processes providing certain Cubans, Haitians, and Nicaraguans who have a supporter in the United States, undergo and clear robust security vetting, and meet other eligibility criteria, to come to the United States in a safe, orderly, and lawful way," a DHS spokesperson told Fox News Digital in a statement on Wednesday. "These processes were built on the success of the process for Venezuelans. These processes are publicly available online, and DHS has been providing regular updates on their use to the public. These processes are part of the Administration’s strategy to combine expanded lawful pathways with stronger consequences to reduce irregular migration, and have kept hundreds of thousands of people from migrating irregularly."

"The CHNV parole processes are public; claims of a secret program are false," they said.

The program faced additional scrutiny last month when it emerged that a Haitian migrant now charged with the rape of a 15-year-old girl in Massachusetts had been flown in via the CHNV program.

"That is something that would have been prevented if they’d just followed the law," DeSantis said.

While the program has been public, announced in a press conference in January 2023 and with monthly data published each month, DeSantis and others have described the program as secret because states are not made aware of who is arriving.

"It is secret because they’re not telling anybody, they don’t tell us anytime someone comes in," he said Wednesday.

The case forms one of a number of legal battles over parole. It has so far shut down two parole policies at the U.S. southern border. Those policies, called "Parole + Alternatives to Detention" and "Parole with conditions," were in place at the southern border to allow migrants to be released into the U.S., and both are on hold pending further litigation in the 11th Circuit Court of Appeals.

Separately, Florida has joined another lawsuit challenging parole releases using the CBP One app at the southern border. The app is used as part of the CHNV program and also to parole up to 1,450 migrants a day at ports of entry.

"We’ve been after them on this parole for a long time, we’ve actually won in court, and it’s our hope we’re going to be able to get that shut down," DeSantis said.