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.

“I think that would be a very dubious move from a constitutional perspective," Collins told "NBC Nightly News with Lester Holt." "Without congressional authorization is not what I think is intended by the National Emergency Act.”

Trump has demanded more than $5 billion to build a border impediment. The president tweeted Wednesday that he had walked out of a "total waste of time" White House meeting with House Speaker Nancy Pelosi, D-Calif., and Senate Minority Leader Chuck Schumer, D-N.Y., after the pair refused to meet his request.

“It makes me very worried about whether we're going to be able to get to a compromise this week," Collins told NBC News. "I'm worried about what the end game is. This cannot be allowed to go on forever.”

Collins suggested earlier this week the Senate vote on two bills passed by the House that could re-open the government. The measures would fund several affected departments and agencies through Sept. 30 and the Department of Homeland Security through Feb. 8. The latter piece of legislation provides only $1.3 billion for border security that cannot be used for a wall.