A number of top Senate Republicans have sent a letter to President Biden protesting efforts to return to the 2015 nuclear deal with Iran and any lifting of sanctions on the Islamic Republic.

The letter comes as Biden officials are participating in indirect talks with Iran and international signatories to the Joint Comprehensive Plan of Action (JCPOA), the formal name for the nuclear deal, on how best to bring the U.S. and Iran back to compliance with the agreement.

The senators, who include senior members of several key committees, called the JCPOA a “failed” agreement and warned against the U.S. giving up leverage by removing sanctions. 

The April 6 letter said the group opposes "any attempt to return to the failed JCPOA, or any deal that offers one-sided concessions to the Iranian regime while it continues to undermine the security of the United States and our allies and partners.”

It was signed by Sen. James Inhofe (Okla.), lead Republican on the Senate Armed Services Committee; Sen. Marco Rubio (R-Fla.), vice chairman of the Senate Intelligence Committee; Sen. Pat Toomey (Pa.), lead Republican on the Senate Banking Committee; and Sen. Todd Young (Ind.), lead Republican on the Senate Foreign Relations Subcommittee on Near East, South Asia, Central Asia, and Counterterrorism.

The letter represents a more pointed rebuke of Biden’s commitment to reenter the deal that former President Trump withdrew from in 2018. The group also voiced support for the Trump sanctions regime.

“The current sanctions in place provide your Administration with an enormous amount of leverage over the Iranian regime, and they should be used as a tool to address all aspects of Iran’s destabilizing behavior,” the senators wrote. 

The Trump administration put in place an estimated 1,500 sanctions following its exit from the deal, reimposing sanctions targeting Iran’s nuclear activities that were lifted as part of the agreement. It levied further sanctions against Iran’s military, financial and oil sectors under the authorities of addressing terrorist activities.

Iran maintains its nuclear activities are peaceful, but it has breached the terms of the JCPOA related to enrichment of uranium — fuel needed to build a bomb. It has built centrifuges that speed up uranium enrichment and has scaled back inspections by international nuclear inspectors. 

The talks in Vienna this week are aimed at creating a road map of “compliance for compliance” where both the U.S. and Iran take steps to roll back their breaches of the agreement. This would involve Biden lifting nuclear-related sanctions and Tehran reversing its nuclear activities. 

Biden has said that he views returning to the JCPOA as the first step in reining in Iran’s nuclear activities and will use that as a starting point to negotiate a “longer and stronger” deal to address issues raised by lawmakers, including Iran’s support for proxy fighting forces, terrorism, its ballistic missile program, human rights abuses and taking of American hostages. 

Republican and Democratic senators have written to the president and senior administration officials expressing unity in opposing any effort by Iran to attain a nuclear weapon and urged the administration to address Iran’s other malign activity.

The president has the support of a critical number of House Democrats for rejoining the nuclear deal as soon as possible.

Opponents of the president’s push to reenter the deal would need a two-thirds majority to override a Biden veto of any legislation aimed at blocking reentry to the deal, a percentage that may be unattainable with so many House Democrats supporting the move.