From Congress:
"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 non-immigrants, or impose on entry of aliens any restrictions may deem to be appropriate."
From SCOTUS:
From the late 19th century through the present day, the Supreme Court has upheld almost every federal immigration regulation against constitutional challenge, citing Congress’s plenary power in this area. As Justice Kennedy wrote in the 2012 decision in Arizona v. United States:
The Government of the United States has broad, undoubted power over the subject of immigration and the status of aliens. … This authority rests, in part, on the National Government’s constitutional power to “establish an uniform Rule of Naturalization,” U. S. Const., Art. I, §8, cl. 4, and its inherent power as sovereign to control and conduct relations with foreign nations….
"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 non-immigrants, or impose on entry of aliens any restrictions may deem to be appropriate."
From SCOTUS:
From the late 19th century through the present day, the Supreme Court has upheld almost every federal immigration regulation against constitutional challenge, citing Congress’s plenary power in this area. As Justice Kennedy wrote in the 2012 decision in Arizona v. United States:
The Government of the United States has broad, undoubted power over the subject of immigration and the status of aliens. … This authority rests, in part, on the National Government’s constitutional power to “establish an uniform Rule of Naturalization,” U. S. Const., Art. I, §8, cl. 4, and its inherent power as sovereign to control and conduct relations with foreign nations….