Iran has repeatedly demonstrated in the past several months that it has access “to restricted U.S. State Department emails or government servers,” according to a letter sent Wednesday to the White House by congressional Republicans and obtained by the Washington Free Beacon.

The series of leaks, which have appeared in Iranian state-controlled propaganda outlets, “constitute a significant security breach of U.S. government property by a foreign adversary” and could indicate there is a mole inside the Biden administration, according to Reps. Kevin Hern (R., Okla.) and Joe Wilson (R., S.C.) and Sen. Bill Hagerty (R., Tenn.). The probe is being handled by the Republican Study Committee, Congress’s largest Republican caucus, and could force the Biden administration into admitting Iran has breached sensitive U.S. networks.

The investigation comes on the heels of a bombshell report Tuesday by Semafor detailing a vast propaganda network linked to the hardline regime in Tehran. That network, known as the Iran Experts Initiative, allegedly includes senior Pentagon official Ariane Tabatabai, as well as other “influential overseas academics” who reported to Iran’s foreign ministry and helped push Tehran’s talking points with American policymakers.