Republican Sen. Susan Collins of Maine is joining a bipartisan effort to terminate a national emergency declaration by President Trump that allows him to divert military funds for the construction of a border wall between the U.S. and Mexico.

Collins, Sen. Jeanne Shaheen, D-N.H., and Sen. Tom Udall, D-N.M., introduced a resolution Wednesday to terminate the declaration, which the lawmakers say violates the U.S. Constitution’s separation of powers clause.

In February, Trump declared a national emergency at the southern border in order to divert funding appropriated for military construction and other projects toward a border wall. The declaration should be terminated because “Congress alone holds the power of the purse,” a news release from Collins’ office said on Wednesday.

The move by Collins could anger fellow Republicans, especially Trump, who has promised since he was a candidate in 2016 that he was going to build a new wall along the southern border. As a candidate, Trump had promised Mexico and not U.S. taxpayers would pay for the wall, but he has since moved to redirect federal money to the project.

Since Trump’s order, the  Department of Defense has said it will divert $3.6 billion from 127 different congressionally appropriated military projects. The money would go instead to the Department of Homeland Security for wall construction.

Both houses of Congress previously voted to terminate the order, but Trump was able to successfully veto the bill, which passed the Senate in March, 59-41. Collins also was in favor of terminating the declaration at the time of the first vote.

Under the National Emergencies Act of 1976, Congress can vote every six months to terminate the declaration.

Collins said in the news release that the move is not because she opposes building the wall or opposes Trump, but because she believes in protecting the U.S. Constitution and the Senate’s rights.

“Let me be clear: The question before us is not whether to support or oppose the wall, or to support or oppose the president. Rather, it is: Do we want the executive branch – now or in the future – to hold a power that the Founders deliberately entrusted to Congress?” Collins said. “I strongly support protecting the institutional prerogatives of the Senate, and the system of checks and balances that is central to the structure of our government.”

Collins said each of the military construction projects that are being waylaid by Trump’s order were recommended by him in his federal budget proposal, which Congress passed and Trump signed into law.

“This bipartisan resolution blocks this overreach, and nothing more, and I urge our colleagues to support it,” Collins said.

Udall said in a prepared statement that Trump’s move was costing New Mexico $125 million in military construction funding alone “and millions more could be at risk if this so-called emergency goes on unchecked. … We must continue to stand up in a bipartisan way to block the president from circumventing Congress and stepping on the separation of powers, or else a new and dangerous precedent will be set.”

Shaheen said Trump’s wall was taking money that had been previously set aside for U.S. troops, their families and military bases meant to protect the national defense.

“These are not slush funds,” Shaheen said. “I appreciate that the Department of Defense made the right call and heeded my concerns about taking funding from the Portsmouth Naval Shipyard; however, Congress needs to take a stand and protect military funding going forward.”