GOP Sen. Susan CollinsSusan Margaret CollinsSenate GOP poised to go 'nuclear' on Trump picks Overnight Health Care: CDC pushes for expanding HIV testing, treatment | Dem group launches ads attacking Trump on Medicare, Medicaid cuts | Hospitals, insurers spar over surprise bills | O'Rourke under pressure from left on Medicare for all Dem group launches ads attacking Trump's 'hypocrisy on Medicare and Medicaid cuts' MORE (Maine) on Wednesday said she would support a resolution to block President TrumpDonald John TrumpTrump mocks wind power: 'When the wind doesn't blow, just turn off the television' Pentagon investigator probing whether acting chief boosted former employer Boeing Trump blasts McCain, bemoans not getting 'thank you' for funeral MORE's emergency declaration to construct the U.S.-Mexico border wall.

Collins, speaking to reporters in Maine, said she would support a resolution of disapproval that was focused on the emergency declaration, which she has described as being of "dubious constitutionality."

“If it’s a ‘clean’ disapproval resolution, I will support it,” she told reporters, according to The Associated Press.

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Collins's comments make her the first Republican senator to say they will back legislation to block Trump's executive action. A spokeswoman for Collins didn't immediately respond to The Hill's request for comment.

But Collins has spoken out strongly against Trump's actions, arguing that the National Emergencies Act wasn't meant to be used to shuffle around money to build a border wall.

"I am strongly opposed to the president invoking his national emergency powers. I don't believe that's what the law was intended to cover," she told a Maine TV station on Tuesday.

Trump announced Friday he was declaring a national emergency for the U.S.-Mexico border wall after Congress passed a funding bill that included $1.375 billion for physical barriers — well below the $5.7 billion requested by the president.

Democrats are expected to force a vote on a resolution of disapproval to block the emergency declaration. The resolution could be filed in the House as soon as Friday, according to the AP.

If the resolution passes the House, where Democrats have a majority, Senate Minority Leader Charles SchumerCharles (Chuck) Ellis SchumerGOP senator: Trump's criticism of McCain 'deplorable' Schumer to introduce bill naming Senate office building after McCain amid Trump uproar Why we need to build gateway now MORE (D-N.Y.) would be able to force a vote in the Senate. If all 47 senators in the Democratic caucus support it, they would need to win over four Republican senators to send the resolution to Trump's desk, where White House officials have indicated he would veto the measure.

Several other Republican senators have raised concerns about, or expressed opposition to, Trump's actions.

Sen. Lisa Murkowski (R-Alaska) said late last week that she didn’t “think that this is a matter that should be declared a national emergency.”

And Sen. Lamar AlexanderAndrew (Lamar) Lamar AlexanderThe next step for justice reform: Ending the ban on federal Pell Grants for eligible students behind bars Senate GOP poised to go 'nuclear' on Trump picks Overnight Health Care: Survey finds 1 in 10 ration medicines to lower costs | Senate Dems call for hearing on Trump abortion rule | Trump health chief backs needle exchanges | Outgoing FDA chief keeps heat on e-cig maker MORE (R-Tenn.) said in a statement after Trump's announcement that the decision was "unwise" because of the precedent it set for future presidents.

"It is inconsistent with the U.S. Constitution because, after the American Revolution against a king, our founders chose not to create a chief executive with the power to tax the people and spend their money any way he chooses," he said. "The Constitution gives that authority exclusively to a Congress elected by the people.”