Dozens of Senate Republicans on Wednesday accused President Joe Biden of violating federal spending law when he froze funding for border wall construction, an action they say gave rise to an uptick in illegal border crossings.

Sen. Richard C. Shelby, R-Ala., ranking member of the Senate Appropriations Committee, Sen. Shelley Moore Capito, R-W.Va., ranking member of that panel’s Homeland Security subcommittee, and 38 other GOP senators wrote to the Government Accountability Office, criticizing Biden’s decision. The president signed an executive order suspending construction on the U.S.-Mexico border wall, and any funding for the project, immediately after his inauguration.

“In the weeks that followed, operational control of our southern border was compromised and a humanitarian and national security crisis has ensued,” the senators wrote. “The President’s actions directly contributed to this unfortunate, yet entirely avoidable, scenario.”

During the Trump administration, the border wall was frequently one of the most contentious issues in government funding debates. The last Homeland Security spending bill, signed into law in December , provided nearly $1.4 billion for the border wall.

The Republican senators said the president’s freeze on construction was a “blatant violation of federal law and infringe(s) on Congress’s constitutional power of the purse.” The lawmakers suggested the administration violated the Impoundment Control Act, a 1974 law establishing procedures to prevent executive branch overreach in congressional funding decisions. The letter requested the GAO’s legal opinion on the matter.

A spokesman for the GAO confirmed the letter had been received, but said requests must undergo a review process before any decision is made.

An official at the Office of Management and Budget said the country has “a right and duty” to secure its borders. 

“But building a massive wall that spans the entire southern border is not a serious policy solution,” the official said in a statement. “The billions of American taxpayer dollars that the previous administration redirected for border wall construction were never appropriated by Congress for that purpose and President Biden’s proclamation makes it quite clear that construction should only be paused to the extent permitted by law.”

Sen. Christopher S. Murphy, the Connecticut Democrat who chairs the Appropriations Subcommittee on Homeland Security, noted the influx of migrants at the southern border didn’t start the day Biden took office.

“This is part of a larger trend that began during the last months of the Trump Administration, all while border wall construction was in progress. We know that building a massive wall and implementing inhumane family separation policies doesn’t work – we hit a 11 year high of apprehensions at the border in 2019 under the worst of Trump’s border policies,” he said in a statement. “President Biden is trying to fix the mess he inherited on immigration in a humane way and I am going to work hard to make sure he has the resources to do that.”

The recent influx of migrants at the southern border has snowballed into a crisis for the White House, which announced last week it would mobilize the Federal Emergency Management Agency to manage growing numbers of unaccompanied children arriving at the border.

Border agents recorded more than 100,000 crossings in February, including more than 9,000 migrant children arriving without their parents, according to data published by U.S. Customs and Border Protection.

The majority of migrants have been expelled under a Trump-administration public health directive. But migrant children are exempted from the order, and the capacity of Health and Human Services Department shelters that house unaccompanied minors after they are picked up by border agents has been strained because of COVID-19 distancing protocols.

“We are on pace to encounter more individuals on the southwest border than we have in the last 20 years,” Homeland Security Secretary Alejandro Mayorkas said Tuesday.

The border crisis comes as Democrats gear up to push for comprehensive immigration legislation, a priority for the White House. The House is set to vote on two immigration bills Thursday: one measure that would grant legal status to undocumented immigrants brought to the U.S. as children and one that would grant legal status to undocumented agricultural workers.