The jihadi terrorist attacks in Paris over the weekend have lit a fire underneath Republicans in Congress looking to assert more control of the nation’s immigration system and block President Obama’s aim to resettle an additional 10,000 refugees from Syria in the United States.

Sens. Jeff Sessions of Alabama and Charles Grassley of Iowa are urging Republican leaders to withhold funding for the refugee admissions program until proper safeguards can be implemented, while Texas Rep. Michael McCaul, chairman of House Homeland Security Committee, urged Obama on Monday to suspend the program altogether.

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The House Judiciary Committee will hold a hearing Thursday examining the U.S. refugee admissions program and Obama’s decision to move to accept additional Syrian refugees — increasing the overall refugee intake ceiling for 2016 by 15,000 to 85,000 — against the advice of top national security experts.

The concerns come amid reports that at least one — and possibly more — of the Paris attackers was an ISIS jihadi posing as a refugee from Syria, entering the European Union through Greece and then making the trek across continental Europe into France.

“In this particular case the high-threat environment demands that we move forward with greater caution in order to protect the American people and to prevent terrorists from reaching our shores,” McCaul wrote in a letter to the president. “In light of the terrorist attack in Paris, I call on you to temporarily suspend the admission of all additional Syrian refugees into the United States pending a full review of the Syrian refugee resettlement program.”

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Earlier in the day on Monday, Obama sought to quell such concerns at a G-20 news conference in Antalya, Turkey, highlighting what he said were the moral imperative of the U.S. to help struggling Syrians.

“As president, my first priority is the safety of the American people. And that’s why, even as we accept more refugees — including Syrians — we do so only after subjecting them to rigorous screening and security checks,” he said.

Critics in Congress and even within his own administration argue that Obama is downplaying the risks and exaggerating the effectiveness of the current vetting procedures.

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However, critics in Congress and even within his own administration argue that Obama is downplaying the risks and exaggerating the effectiveness of the current vetting procedures.

Many law enforcement officials, including FBI Director James Comey, have conceded that the U.S. government lacks the resources needed to properly weed out radicals who may be masquerading as refugees.

Related: Hundreds of Syrians Cross Border

In the Senate, Sessions launched a fresh push Monday to block funding of the president’s refugee resettlement plan until the costs of the program are accounted and paid for and Congress approves of the program.

He warned that by not standing its ground, the Senate was effectively giving Obama a “blank check” to finance the program. He also noted that the White House’s stated cost for the program, $1.2 billion, was significantly less than outside projections, such as one from Heritage Foundation estimating that the net cost of resettling the 10,000 refugees would be $6.5 billion over the course of their lives. Most refugees are afforded benefits such as food stamps, healthcare and retirement that were left out of the president’s calculations.

Sessions’s move piggybacks off a similar push by Grassley earlier this month to block funding any resettlement plan until a comprehensive process for vetting potential refugees and filtering out terrorists could be implemented.

Momentum is also building in the House to thwart the resettlement plan at all costs.

Momentum is also building in the House to thwart the resettlement plan at all costs.

“There’s no possible way to screen them,” House Intelligence Committee Chairman Devin Nunes said Sunday on CBS “Face the Nation.”

A House Judiciary committee aide expressed concern over Obama’s insistence on following through with the scheme in light of the recent events in Paris, noting that ISIS terrorists and sympathizers have explicitly stated their intentions to use the refugee system to infiltrate Western countries and are now fulfilling those ambitions.

Meanwhile, a growing number state governors have stated that they will not accept any Syrian refugees under Obama’s resettlement plan.

“Heck, we may take them to the University of Missouri,” Republican presidential candidate Mike Huckabee, the former governor of Arkansas, said Saturday in a radio interview . “A lot of the students are so stressed out from feeling unsafe because somebody said a word they didn’t like that they are not using their dorm rooms anymore. Maybe we can put them there.”