A majority of House lawmakers now support a resolution to reject the recently signed nuclear agreement with Iran, marking another blow to the White House’s aggressive push to convince Congress to back the deal, according to sources on Capitol Hill.

At least 218 Republican lawmakers have signed on to support a resolution expressing "firm disapproval" of the nuclear deal, which would provide Iran with billions of dollars in sanctions relief while enabling it to continue work on ballistic missiles and other nuclear research.

The measure, which is being led by Rep. Peter Roskam (R., Ill) and was first reported by the Washington Free Beacon, comes as Congress takes 60 days to review the deal before voting on it.

Many lawmakers, including a growing number of Democrats, have come out against the deal, citing concerns it does not do enough to limit Iran’s nuclear program.

Critics remain most concerned about portions of the deal that will ban U.S. inspectors from Iran’s nuclear sites and remove restrictions on the Islamic Republic’s ballistic missile program.

The Obama administration has launched an aggressive push to sell the deal, both on Capitol Hill and among the public. President Barack Obama and other senior administration officials have been holding conference calls with liberal groups to sell the deal and put pressure on Congress.

Support for the resolution rejecting the deal is a sign that many lawmakers have made up their minds well before the congressional review period expires.

At least three members of the House leadership, as well as 18 of 22 House committee chairmen and 23 of the 25 GOP members of the House Foreign Affairs Committee, have already signed on to back the resolution, according to figures provided by congressional sources.

House Freedom Caucus Chair Jim Jordan (R., Ohio) and Republican Study Committee Chair Bill Flores (R., Texas) also back the measure.

More and more lawmakers are deciding to oppose the deal on a daily basis, Roskam told the Free Beacon.

"Time is not the friend of this deal. The more time Members spend evaluating this agreement, the more they realize it's an historic mistake," Roskam said. "While the administration continues to flaunt a false choice between this deal and war, Secretary [John] Kerry said repeatedly over the course of the negotiations that he would walk away from a bad deal."

However, "if that was the case, then surely there was an alternative besides this dangerous agreement and war," Roskam said. "Congress and the American people believe a better agreement is still achievable, and we can start by walking away from this one. This is why a majority of the House is already prepared to vote against this deal."

Congress will "do everything in our power to shut down an accord that so utterly fails to shut down Iran's nuclear program," he said.

The resolution explicitly states that Congress disapproves of the nuclear deal and reiterates support to stop Iran from building a nuclear weapon.

The resolution also rejects key portions of the deal, including ones that provide Iran billions of dollars in assets and approve the Islamic Republic’s right to construct ballistic missiles and freely purchase arms.

In addition, it highlights that the deal "allows key restraints on Iran’s nuclear program to expire within 10 to 15 years, including those on Iran’s domestic uranium enrichment program and heavy-water reactor at Arak."

"The Joint Comprehensive Plan of Action [JCPOA] fails to address Iran’s egregious human rights record, Iran’s role as the world’s leading state sponsor of international terrorism, and Iran’s unjust imprisonment of innocent United States citizens," the resolution states.

Roskam has spoken to colleagues about the resolution since spearheading it several weeks ago, according to sources familiar with the situation. The lawmaker spent most of last week on the floor wrangling support for the resolution.

Rep. Mac Thornberry (R., Texas), chair of the powerful Armed Services Committee, became the 218th co-sponsor of the resolution on Friday, when he called Roskam to lend his support, sources said.

Thornberry had been withholding judgment of the deal until he was able to grill senior Obama administration officials about it during a hearing last week.

Roskam will speak to House Democrats about the measure over the August recess to secure a veto-proof majority, sources said.

A senior congressional aide familiar with the effort said the administration is failing to convince lawmakers to back the deal.

"It appears the administration’s sales pitch for this deal is falling on deaf ears. Closed-door briefings and public hearings have apparently left Members with more questions than answers, and the administration’s decision to circumvent Congress by first bringing the deal to the UN infuriated key Democrats who are otherwise loyal to the president," the source said.

"This level of opposition so early in the review period indicates that Congress really has a chance of killing the agreement. What Congressman Roskam has done—securing 218 commitments from Members vote against the deal in just two weeks—is a rather remarkable feat. He still has more work to do, but this is an impressive start," the source added.

In the weeks since the deal was signed, critics have warned that it will only embolden Tehran’s intransigence, including its illicit nuclear relationship with North Korea.

Meanwhile, Iranian officials have downplayed comments by the Obama administration maintaining that the deal shuts down Iran’s pathway to the bomb while imposing a strict inspections regime.

Hamid Baeidinejad, an official in the Iranian foreign ministry and one of the country’s nuclear negotiators, claimed in an interview that "the remarks by the western officials are ambiguous comments which are merely uttered for domestic use and therefore we should say that there is no ambiguity in this [nuclear] agreement."