President Donald Trump said on Monday evening that he intended to close the US to people trying to immigrate into the country to live and work, a drastic move that he said would protect American workers from foreign competition once his country’s economy begins to recover from the shutdown caused by the coronavirus outbreak.

“In light of the attack from the Invisible Enemy, as well as the need to protect the jobs of our GREAT American Citizens,” Trump tweeted, “I will be signing an Executive Order to temporarily suspend immigration into the United States!”

On Tuesday, a Homeland Security official said that the executive order was still being drafted and that details of the potential ban, including on specific exemptions, were subject to change.

Late on Monday, several people had said a formal order temporarily barring the provision of new green cards and work visas could come as early as in the next few days.

Under such an executive order, the Trump administration would no longer approve any applications from foreigners to live and work in the US for an undetermined period of time, effectively shutting down the legal immigration system in the same way the President has long advocated closing the borders to illegal immigration.

It also emerged that the President’s late-night tweet caught some top Homeland Security officials off guard. The legal authority for the move was being evaluated on Tuesday by lawyers at the Department of Justice.

It is not clear how long the review will take or when Trump intends to make the formal announcement, though an announcement is expected this week.

Trump’s tweet left many questions unanswered. The White House provided few details about what would be a drastic move to close the country to people seeking to move to America to work or join family members, but cast the announcement as an attempt to reduce competition for jobs as states reopen from the coronavirus shutdown.

It was unclear what legal authority the President will claim to shut off immigration, even temporarily.

The number of visas issued to foreigners abroad looking to immigrate to the US has declined by about 25 per cent, to 462,422 in the 2019 fiscal year from 617,752 in 2016.

Even before the President’s tweet, the Trump administration had expanded travel restrictions, slowed visa processing and moved to swiftly bar asylum seekers and undocumented immigrants from entering the country, alarming immigration advocates who have said that Trump and his advisers are using a global pandemic to further hard-line immigration policies.

Several people familiar with the President’s plans said the Department of Homeland Security was separately weighing a large expansion of travel restrictions that already prohibited travellers from Europe and China. The restrictions would significantly shrink the number of people able to come to the US for short-term visits.

Trump and his advisers have argued inside the White House that doing more to bar people from other countries from coming into the US, either for short-term visits or to live and work in the country for longer periods, could help limit the number of infected people who arrive from potential coronavirus hotspots around the world. And they argue that it could relieve pressure on the American healthcare system.