Kentucky Sen. Rand Paul reportedly said Saturday he would vote in favor of a resolution blocking President Donald Trump's national emergency declaration.

Paul joins three other Republican senators who announced their support of blocking the emergency, creating a likely majority in the Senate to pass the bill.

Trump has already said he would veto the motion, which would mark the first of his presidency.

Kentucky Sen. Rand Paul said he would vote in favor of blocking President Donald Trump's national emergency declaration, according to the Bowling Green Daily News.

Paul reportedly said in a speech to nearly 200 Republicans Saturday that he objected to allowing Trump to exercise "extra-Constitutional powers" by using the national emergency to secure funds to build his long-touted wall along the US-Mexico border.

"I can't vote to give the president the power to spend money that hasn’t been appropriated by Congress," Paul said. "We may want more money for border security, but Congress didn't authorize it. If we take away those checks and balances, it's a dangerous thing."

Paul joins Republican lawmakers, including Maine Sen. Susan Collins, Alaska Sen. Lisa Murkowski and North Carolina Sen. Thom Tillis, who announced they would vote to block the emergency last week.

Trump has already said he would veto the motion if it passes, setting the stage for a two-thirds majority override vote in each chamber of Congress.

Read more: Here are the GOP lawmakers breaking with Trump over his national-emergency declaration

Trump initially declared a national emergency on February 15 to secure funds for the border wall.

Democrats were quick to object to the action, and a growing number of Republican lawmakers have spoken out about their concerns that it would set a precedent that future presidents could declare emergencies to further their personal policy desires.

Concerns about the move are not cleanly split between party lines. Republican Sen. Ron Johnson said on NBC's "Meet the Press" days after the declaration that "many of us are concerned about" the declaration.

Though the declaration is similar to "the expansion of authority Congress has given past presidents," Johnson said he wished "he wouldn't use it in this case. But again, I understand his frustration."

The chairman of the Senate Homeland Security and Governmental Affairs Committee said he would take a "careful look" at how the funding battle plays out along with Trump's plan for the money.