President Donald Trump said Tuesday that starting Feb. 1, he will deny federal funding to any states that are home to local governments resisting his administration’s immigration policies, expanding on previous threats to cut off resources to the so-called sanctuary cities themselves.

Such an action could have far-reaching impacts across the U.S., potentially even in places that aren’t particularly friendly to noncitizens.

Two previous efforts by Trump to cut off some funding for sanctuary jurisdictions were shut down by courts.

Trump unveiled the concept this time late in a speech Tuesday at the Detroit Economic Club, without offering specifics.

“Starting Feb. 1, we’re not making any payments to sanctuary cities or states having sanctuary cities, because they do everything possible to protect criminals at the expense of American citizens and it breeds fraud and crime and all of the other problems that come,” he said. “So we’re not making any payment to anybody that supports sanctuary cities.”

Back in Washington, Trump was asked by reporters what kind of funding would be affected on Feb 1: “You’ll see,” he said. “It’ll be significant.”

There is no strict definition for sanctuary policies or sanctuary cities, but the terms generally describe limited cooperation with Immigration and Customs Enforcement.

Courts have rejected the idea before

In executive orders last year, the president directed federal officials to withhold money from sanctuary jurisdictions that seek to shield people in the country illegally from deportation.

A California-based federal judge struck it down despite government lawyers saying it was too early to stop the plan when no action had been taken and no specific conditions had been laid out.

In Trump’s first term in office, in 2017, courts struck down his effort to cut funding to the cities.

Some of the details are tricky

The Justice Department last year published a list of three dozen states, cities, and counties that it considers to be sanctuary jurisdictions. The list is overwhelmingly made up of places where the governments are controlled by Democrats, including the states of California, Connecticut, and New York, cities such as Boston and New York, and counties including Baltimore County, Maryland, and Cook County, Illinois.

The administration has been threatening funding in specific places. The federal government has moved to halt funding for a variety of programs in recent weeks and is already facing legal challenges.

The U.S. Department of Health and Social Services announced last week that it was halting money from five Democratic-led states for daycare subsidies and other aid to low-income families with children over unspecified suspicions about fraud. A court put that on hold.