https://www.law.cornell.edu/uscode/text/8/1182
(f) Suspension of entry or imposition of restrictions by President
Whenever the President finds that the entry of any aliens or of any
class of aliens into the United States would be detrimental to the
interests of the United States, he may by proclamation, and for such
period as he shall deem necessary, suspend the entry of all aliens or
any class of aliens as immigrants or nonimmigrants, or impose on the
entry of aliens any restrictions he may deem to be appropriate. Whenever
the Attorney General finds that a commercial airline has failed to
comply with regulations of the Attorney General relating to requirements
of airlines for the detection of fraudulent documents used by
passengers traveling to the United States (including the training of
personnel in such detection), the Attorney General may suspend the entry
of some or all aliens transported to the United States by such airline.