WASHINGTON (Reuters) - President Donald Trump on Wednesday ordered a temporary block on some foreigners from permanent residence in the United States, saying he wanted to protect American workers and jobs during the coronavirus pandemic.

U.S. President Donald Trump addresses the daily coronavirus task force briefing at the White House in Washington, U.S., April 21, 2020. REUTERS/Jonathan Ernst

The order, an election-year move likely to prove popular with his conservative base, is to last for 60 days and then will be reviewed and possibly extended. It is likely to face legal challenges.

Some critics saw Republican Trump’s announcement as a move to take advantage of the coronavirus crisis to implement a long-sought policy goal of barring more immigrants in line with his “America first” platform.

“In order to protect our great American workers I have just signed an executive order temporarily suspending immigration into the United States. This will ensure that unemployed Americans of all backgrounds will be first in line for jobs as our economy reopens,” Trump said at his daily news conference about the coronavirus at the White House.

He also said it will “preserve our healthcare resources for American patients” afflicted by the coronavirus.

Trump’s order could block more than 20,000 people per month from obtaining a green card of permanent residence, based on an analysis by the Washington-based Migration Policy Institute.

However, U.S. immigration services abroad and at home have largely come to a halt in the pandemic, which may blunt the immediate effect of the order.

Democrats and immigrant advocates have criticized the new policy as an attempt to distract from Trump’s response to the pandemic. The United States has the most confirmed cases and deaths in the world with at least 821,000 people infected and at least 46,000 deaths, according to a Reuters tally.

The measure would block immigration based on both employment and family ties, but not affect guest workers who enter the United States on temporary visas, such as farm workers and skilled workers in the H-1B visa program.

Doctors, nurses and other healthcare professionals will be exempted, as will other prospective immigrants coming to the country to perform “essential” work to combat the new coronavirus, as determined by federal agencies.

The measure also excludes immigrants applying for the EB-5 visa program, which allows foreigners willing to invest in U.S. projects that create or preserve jobs to obtain permanent residence.

The order blocks the ability of relatives of U.S. citizens to seek permanent residence through their familial connections, if those relatives are outside the United States. But it makes an exception for spouses of U.S. citizens and unmarried children under the age of 21.

Omar Jadwat, director of the American Civil Liberties Union’s Immigrants’ Rights Project, said that while the order is limited in scope, it “will cause real pain for families and employers across the country.”

White House lawyers worked all day to craft the language for the order, prompting some officials to say the signing might have to wait for Thursday. But aides described Trump as eager to sign the document.

Trump won the White House in 2016 in part on a promise to crack down on immigration and has made the issue central to his presidency. But many of his major moves trying to curb immigration have been challenged in court.

A person familiar with the internal debate at the White House said Trump and his advisers had discussed the executive order over the weekend and that the move was directed at his electoral base.

“He’s wanted this all along,” the person said. “But now under this pandemic he can absolutely do it.”

Trump signaled his intentions in a Twitter post on Monday and immigration attorneys representing businesses argued it would only further depress the economy.

Michael Clemens, a senior fellow at the Washington-based Center for Global Development, said that a range of industries would be hurt including ones that are critical during a public health emergency such as food processing, warehousing, shipping, eldercare, childcare, communication and technology.

Many of those jobs are filled by immigrants and the family members they reunite with from abroad, he said.