President Trump’s revision of his controversial executive order imposing a travel and refugee ban on certain countries will get an important legal test on Monday, when a federal appeals court in Virginia weighs whether the administration overstepped its authority.

At issue is whether the ban violates the Religion Clause of the First Amendment, the Due Process Clause of the Fifth and 14th Amendments, and the ban on nationality discrimination in the issuance of immigrant visas contained in a 65-year-old congressional law.

The case will be a major test of presidential power, especially in the area of immigration.

The White House frames the issue as a temporary move involving national security. A coalition of groups in opposition call the order blatant religious discrimination, since the six countries involved have mostly Muslim populations: Iran, Libya, Somalia, Sudan, Syria, and Yemen.