U.S. immigration officials have been revoking visas for weeks, even before President Trump Donald John TrumpHR McMaster says president's policy to withdraw troops from Afghanistan is 'unwise' Cast of 'Parks and Rec' reunite for virtual town hall to address Wisconsin voters Biden says Trump should step down over coronavirus response MORE signed an executive banning people from Muslim-majority countries from entering the U.S., NBC News reports.

As many as 40 individuals with student visas have been blocked from reentering the country since early this year. Many of them were returning to the U.S. after visiting their home countries for winter break.

It wasn’t clear whether the visa cancellations had anything to do with the Trump administration or the president’s executive order, though the students that have run into issues are not from the countries explicitly targeted by action.

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International students who had their visas revoked earlier this month were told upon arrival in the U.S. that they would either have to return to their country of origin or face criminal charges.

One official told NBC that immigration officials could have been applying policies they assumed would be implemented under Trump.

Trump’s executive order bans people from Iraq, Iran, Syria, Yemen, Libya, Sudan and Somalia from traveling to the U.S. Some U.S. officials warned international students traveling to the designated countries that they could be blocked from reentering the U.S., even with a valid visa.

"My advice to anyone holding a visa from any of these countries is do not go home because you will not get back in," one official told NBC.

Trump’s executive order also put a 120-day moratorium on the country’s refugee resettlement program. Reports began circulating almost immediately after the president signed the action that refugees arriving in the U.S. were being detained.