In the wake of President Donald Trump’s decision Friday to declare a national emergency to fund a wall along the U.S.-Mexico border, U.S. Rep. Dan Newhouse voiced concerns over the legality of the decision.

The 4th District Republican lawmaker, who represents the Yakima Valley, said he supports the goal of further securing the border between the two countries, but declaring an emergency “requires fully vetting the President’s request.”

“I support President Trump’s goal to secure the southern border. However, I have concerns about this initial announcement and have several questions for the White House about its authority to reprogram funds for this purpose,” he said in a statement.

The declaration comes after Trump agreed to sign a spending bill to avoid a second government shutdown after Congress denied the president’s $5.7 billion border fund request for a 234-mile steel wall. The approved budget included $1.375 billion for roughly 55 miles of fencing.

The administration has been eyeing several pots of money — including disaster funds, counternarcotic accounts and military construction dollars — to fund the wall, according to congressional aides and White House officials, the Associated Press reported.

“While many past presidents have declared national emergencies, it is exceedingly rare that funds have been reprogrammed for such declarations,” Newhouse said Friday. “It is my firm belief that only Congress has the duty to decide how taxpayer dollars are spent. The seriousness of this issue requires fully vetting the president’s request to ensure we are holding steadfast to our nation’s founding document.”

“We cannot create a slippery slope by setting a precedent that violates the Constitution’s separation of powers,” Newhouse added.

Newhouse voted in favor the spending bill and border security deal on Thursday.

Sen. Patty Murray, a Democrat, sharply criticized Trump's action on Thursday, calling it an "outrageous, horrific, and un-American abuse of power."

Washington state Attorney General Bob Ferguson, who has sued the administration nearly 30 times since Trump was sworn in as president, released a statement calling the president’s announcement unlawful.

“We are working with members of our congressional delegation to determine if this action depletes federal funds flowing to Washington,” he said. “If Washington is harmed, my office will take appropriate steps to block this unlawful action, just as we’ve blocked more than a dozen illegal and unconstitutional policies of this president.”