A bipartisan group of senators called on the governments of the United Kingdom, France and Germany to take action to halt the expiration of the United Nations’ sanctions on Iran’s missile and drone programs in a letter on Friday addressed to the three countries’ ambassadors.

A letter, signed by 31 lawmakers including the senior members of the Senate Foreign Relations Committee, praises the E3 nations for their recent announcement of their plans to unilaterally maintain their sanctions, but argues that U.N. action is necessary to maintain proper safeguards on Iran.

Under the 2015 nuclear deal, the U.N. sanctions on Iran’s missile and drone programs will expire next month, and the E3 countries — the only nations with the ability to intervene at the U.N. to keep the sanctions in place — have said they do not plan to do so.

“Allowing these restrictions to expire poses a threat to stability and security in the Middle East and beyond,” the letter reads. “It would enable the further proliferation of advanced weaponry, empower malign actors in the Middle East and Europe, and send the wrong signal to the Iranian regime when it has shown no willingness to alter its destabilizing policies across a number of areas.”

The letter highlights Iran’s expanding nuclear program, domestic repression and proliferation of missiles and drones to proxies in the region and to Russia.

“Without the force of a binding UN Security Council resolution, there is no multilateral framework that mandates international sanctions on Iran’s missile and drone program,” the senators wrote. “We strongly support the decision to take steps that would maintain sanctions on Iran’s missile and drone program before UN sanctions sunset in mid-October, and we encourage you to urge other European allies and other like-minded partners to do the same.”

The senators note that the expiration of U.N. sanctions would permit Iran to provide Russia with missiles that could “could hit targets across the entirety of Ukraine, as well as credibly threaten most of mainland Europe.”

Sens. Bob Menendez (D-NJ) and Bill Hagerty (R-TN) organized the letter, which was also signed by Sens. Ben Cardin (D-MD), Jim Risch (R-ID), Jeanne Shaheen (D-NH), Tim Scott (R-SC), Tim Kaine (D-VA), Roger Wicker (R-MS), Maggie Hassan (D-NH), John Barrasso (R-WY), Catherine Cortez-Masto (D-NV), John Cornyn (R-TX), Bob Casey (D-PA), Marco Rubio (R-FL), John Fetterman (D-PA), Chuck Grassley (R-IA), Amy Klobuchar (D-MN), Mike Braun (R-IN), Michael Bennet (D-CO), John Kennedy (R-LA), Jacky Rosen (D-NV), Lindsay Graham (R-SC), Richard Blumenthal (D-CT), Todd Young (R-IN), Chris Coons (D-DE), Jerry Moran (R-KS), Cory Booker (D-NJ), Joni Ernst (R-IA), John Hoeven (R-ND), Steve Daines (R-MT) and Deb Fischer (R-NE).

A previous letter from 26 senators in June urged the administration to work with the E3 to initiate snapback if Iran enriched uranium to 90% purity or higher.

The letter was released shortly after news broke that Menendez had been indicted on federal bribery charges.