President Donald Trump’s effort to bar travelers from seven mostly Muslim nations is on a track to the U.S. Supreme Court, which may eventually decide how much authority the executive branch has on immigration and national security.

The ban affecting business travelers, students, immigrants and refugees may be re-imposed as early as Monday if an appeals court puts on hold a judge’s order blocking it while the legal fight continues.

“Overturning the ruling would cause such anguish and confusion at the borders,” said Jayashri Srikantiah, a Stanford Law School professor who specializes in immigration. She said it’s “extremely hard to bet” as to what the appeals court will do, “but one can imagine the confusion caused by reversing the TRO is something the court is taking into consideration.”