President Donald Trump said that he is suspending immigration to the United States in response to the current global pandemic and the need to protect jobs.

In a tweet Monday night, the president attributed the suspension to an “attack from The Invisible Enemy” and the “need to protect the jobs of our GREAT American Citizens.”

He added that he would sign an executive order suspending immigration.

Trump previously restricted travel from China and Europe to stop the spread of the coronavirus.

It’s not clear from the president’s tweet whether the order would bar non-U.S. citizens from traveling to the country for purposes such as business or to visit family.

White House officials offered few details Monday night.

The move “had been under consideration for a while,” a senior administration official told NBC News. The official said that although Trump believes the U.S. is winning the fight against the coronavirus, he also thinks it is important to make every effort to get ahead and protect the borders to prevent further spread.

The official said details about how the plan would be implemented and how many countries would be affected “will be forthcoming.”

The executive order could be signed as early as this week, according to the administration official, who did not offer any details about whether it had been drafted or where the process stands.

Immigration has long been an issue that has energized the president’s core supporters, and Monday night’s tweet will undoubtedly be no different.

Immigration to the U.S. is already functionally shut down. The Trump administration had closed the U.S. Canada border and started deporting asylum-seekers and other migrants on the southern border without due process. International air travel has primarily been suspended.

Immigration advocates and activists criticized Trump’s announcement, calling the move radical and unprecedented.

“The implication is that immigrants are a threat to the American economy, but we know the exact opposite to be true,” said Krish O’Mara Vignarajah, president and CEO of Lutheran Immigration and Refugee Service. “While immigrants across America are on the front lines risking their lives to save ours, it is simply unconscionable to scapegoat immigrants for this pandemic.”

Sen. Kamala Harris, D-Calif., said the president was taking advantage of the situation to push his hard-line immigration policies.

“Trump failed to take this crisis seriously from day 1. The abandonment of his role as president has cost lives. And now, he’s shamelessly politicizing this pandemic to double down on his anti-immigrant agenda,” Harris tweeted.

The president said last month that he was discussing closing the country’s borders with Mexico and Canada because of the virus. A senior official said then that the administration was exploring new restrictions amid fears that large numbers of Central Americans would try to access the U.S. health care system illegally.