GOP Sen. Susan CollinsSusan Margaret CollinsDemocratic senator to party: 'A little message discipline wouldn't kill us' Poll: 57 percent of Americans think next president, Senate should fill Ginsburg vacancy On The Trail: Making sense of this week's polling tsunami MORE (Maine) on Wednesday said she would support a resolution to block President TrumpDonald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick 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 SchumerChuck SchumerPelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' 3 reasons why Biden is misreading the politics of court packing Cruz blocks amended resolution honoring Ginsburg over language about her dying wish 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 AlexanderPelosi urges early voting to counter GOP's high court gambit: 'There has to be a price to pay' Graham: GOP has votes to confirm Trump's Supreme Court nominee before the election The Hill's Morning Report - Sponsored by Facebook - Washington on edge amid SCOTUS vacancy 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.”