President Donald Trump said he’ll sign an executive order temporarily suspending immigration into the U.S. as the country tries to contain the spread of the coronavirus.

Trump made the announcement by tweet late Monday night, and did not offer specifics, such as the time frame or the scope of who would be affected. The White House did not immediately respond to a request for comment.

He tweeted that he made the decision, “in light of the attack from the Invisible Enemy, as well as the need to protect the jobs of our GREAT American Citizens.”

It’s the latest measure taken by Trump and his administration to restrict the U.S. border amid the pandemic. Trump has imposed broad travel restrictions on China, Europe, Canada and Mexico to curb the virus’s spread, and the State Department last month temporarily suspended routine visa services at embassies and consulates.

The U.S. Citizenship and Immigration Services has also already suspended routine in-person services, but is still offering some emergency services.

Trump’s tweet raised the prospect of an order freezing all new applications from foreigners to live and work in the U.S., potentially shutting down the legal immigration system as the president and his advisers have already restricted international travel and long pushed to close borders to entry of undocumented migrants. Whether he’ll consider certain exemptions is unclear -- the administration has worked recently to still allow farm workers in from Mexico, for instance.

At the same time, the White House has ordered federal agencies to begin preparing to return workers to offices and begun to reopen parts of the country, despite a widespread shortage of testing and warnings of a second wave.

The president has often said the pandemic has strengthened his desire to further restrict access to the U.S., and even to manufacture certain products on home soil.

Cracking down on illegal immigration and a promise to erect a wall at the Mexican border formed the centerpiece of Trump’s election campaign in 2016.

His Gallup approval rating slipped six points last week as scrutiny of his handling of the outbreak has intensified, and the U.S. leads the world in total reported cases.

Congressman Joaquin Castro, a Texas Democrat and chairman of the Congressional Hispanic Caucus, wrote on Twitter that the suspension was “not only an attempt to divert attention away from Trump’s failure to stop the spread of the coronavirus and save lives, but an authoritarian-like move to take advantage of a crisis and advance his anti-immigrant agenda.”

Since becoming president, Trump has sought to curb immigration and migration widely -- restricting travel from certain majority-Muslim nations, pushing to erect the wall, striking deals to almost immediately deport asylum seekers from certain countries and moving to slash the number of refugees that the U.S. accepts. He’s also repeatedly criticized leaders of so-called sanctuary cities and mused about trying to end automatic citizenship for people born in the U.S.

His previous travel restrictions have been swiftly met with legal challenges.