Sen. Susan Collins, R-Maine, on Wednesday questioned the constitutionality of President Trump declaring a national emergency at the southern border as a way to build his promised wall.

Trump is rumored to want to use the National Emergencies Act of 1976 to push forward with the construction of a physical barrier along the U.S.-Mexico border. The law would allow him to use military funding to undertake the project, despite Democratic opposition to the wall that has led to a 19-day partial government shutdown over funding.