Expelling Member of Congress

U.S. Constitution - Article 1 Section 5

Article 1 - The Legislative Branch

Section 5 - Membership, Rules, Journals, Adjournment

Each House may determine the Rules of its Proceedings, punish its Members for disorderly Behavior, and, with the Concurrence of two-thirds, expel a Member.

https://www.usconstitution.net/xconst_A1Sec5.html