Senate Republicans want to block the Export-Import Bank from being able to provide help to Iran.

Sen. Marco Rubio has introduced legislation that would close a “loophole,” which the Florida Republican argues currently allows the country to get indirect financing from the bank.

{mosads}The Ex-Im Bank, according to the bill, would not be allowed to “guarantee, insure, or extend… credit” for a transaction that involves anyone financially linked to the Iranian government, a government-created business or “an operation in Iran.”

The legislation—which is backed by GOP Sens. John Cornyn (Texas), Tom Cotton (Ark.) and Ted Cruz (Texas)—could upend a deal for Boeing to sell passenger aircraft to Iran.

Rubio said the Boeing sale, and a separate Airbus deal, could help “further Iran’s promotion of terrorism.”

“Taxpayer dollars should not be used to fund Iran’s purchase of new aircraft which it will use to ship weapons and troops to brutal regimes and terrorist groups,” he added in a statement. “Congress should stop this from happening by passing this legislation.”

Republicans argue current law allows the bank to provide indirect access to deals that bolster Iran, including the sale of U.S.-made aircraft and equipment.

The House voted to block the Boeing sale late last week as part of the Financial Services and General Government Appropriations Act.

Timothy Keating, Boeing’s senior vice president of government operations, said late last month that the company “will make no effort” to involve the Export-Import Bank in the sale.

“As you know, the U.S. Export-Import Bank is prohibited from any dealings with Iran, so that agency will not be a financing option that is pursued by the costumer,” he wrote in a letter to Reps. Peter Roskam (R-Ill.) and Rep. Jeb Hensarling (R-Texas). 

Rubio joined Senate Republicans in opposing the Iran nuclear deal last year and has supported a string of proposals looking to crack down on Iran and toughen sanctions in the wake of the agreement.

Rubio added in his statement that since the deal the “Iranian regime has done nothing to modify its provocative, anti-American behavior.”