Amid growing reports that the Biden administration is engaging in discussions with Iran over its nuclear program, a bipartisan group of 26 senators wrote to President Joe Biden urging him to pursue stronger deterrence of Iran and warning against an ineffective agreement.

The letter, promoted by AIPAC during a lobbying mission earlier this month, was drafted ahead of recent revelations of talks between the U.S. and Iran. Its signatories include a handful of Democratic lawmakers who were supportive of the 2015 nuclear deal and efforts to rejoin it earlier in Biden’s presidency — indicating that Biden cannot necessarily count on widespread support from the Democratic side of the aisle for a new agreement.

“Congress stands united behind the long held bipartisan position that Iran must never be allowed to obtain a nuclear weapon,” the letter reads. “It is crucial for your administration to remain aligned with Congressional efforts related to Iran’s nuclear program and not agree to a pact that fails to achieve our nation’s critical interests. We urge you to take meaningful steps to curb Iran’s destabilizing activities and deter the regime from pursuing this nefarious ambition any further.”

The letter urges Biden to step up U.S. deterrence — a posture that would seem contrary to rumors that the administration is willing to ease sanctions or sanctions enforcement on the regime in response to a freeze in its nuclear enrichment. Critics charge that the administration seeks to avoid congressional oversight of a new arrangement with Iran.

“It is imperative today that we strengthen our efforts to deter Iran from achieving nuclear weapons capability. We must make Iran understand, in no uncertain terms, that further advances in its nuclear program will be met with unified international action,” the letter continues. “Iran simply cannot be allowed to advance its nuclear program with impunity and the [People’s Republic of China] cannot be given a pass for accelerating Iran’s destabilizing behavior. We urge you to restore this posture of deterrence and provide leadership to strengthen the resolve of the international community.”

The letter was led by Sens. Kirsten Gillibrand (D-NY) and James Lankford (R-OK). They were joined by Democratic Sens. Jacky Rosen (D-NV), Gary Peters (D-MI), Richard Blumenthal (D-CT), Joe Manchin (D-WV), Alex Padilla (D-CA), Maggie Hassan (D-NH), Raphael Warnock (D-GA), Mark Kelly (D-AZ), Ron Wyden (D-OR) and Michael Bennet (D-CO).

Notably, Peters, Blumenthal, Hassan, Warnock, Kelly, Wyden and Bennet were supportive of the original Iran deal and/or efforts to rejoin it earlier in Biden’s term. Padilla, who was not in the Senate at the time of the original 2015 agreement, does not appear to have publicized his opinion on the original deal or efforts to reenter it.

Republican Sens. Chuck Grassley (R-IA), Shelley Moore Capito (R-WV), Susan Collins (R-ME), Mike Crapo (R-ID), John Boozman (R-AR), Bill Cassidy (R-LA), Rick Scott (R-FL), Mike Braun (R-IN), Jerry Moran (R-KS), Pete Ricketts (R-NE), John Kennedy (R-LA), John Hoeven (R-ND) and Dan Sullivan (R-AK) also signed on. Sen. Kyrsten Sinema (I-AZ) also joined the letter.

The lawmakers further encouraged Biden to secure commitments from European allies to snap back United Nations sanctions on Iran should the regime pass the weapons-grade enrichment threshold of 90%.

“Such a move would squeeze Iran’s revenue sources and serve notice that Iran cannot continue to reap the benefits of international sanctions relief while progressing towards the development of a nuclear weapon,” the letter reads.