U.S. Senators Elizabeth Warren, D-Mass., and Roger Marshall, R-Kan., probed the Biden administration for more information on what authorities they have to stop the use of crypto to evade sanctions.

The two aired concerns specifically about the stablecoin Tether, in a letter sent over the weekend to Defense Secretary Lloyd Austin, Treasury Secretary Janet Yellen and Under Secretary for Terrorism and Financial Intelligence Brian Nelson, among other officials.

“We write with heightened concerns about rogue nations’—including Russia, Iran, and North Korea—reliance on cryptocurrency to evade sanctions,” Warren and Marshall said. “The national security threat posed by cryptocurrency requires a commensurate response by our country’s defense community.”

Treasury has brought multiple sanctions …