loyalty oath

noun

: a usually mandatory oath affirming the loyalty of its taker (as to a sovereign, government, or party principles)

ruled the Genevese … with the help of loyalty oaths and the gibbet—

Times Literary Supplement

the loyalty oath will be abandoned at the next Democratic convention—

Newsweek

especially : an oath often required of public employees or applicants for public employment in the U.S. typically affirming that the signer upholds the U.S. or state constitutions and is not knowingly a member of any of a number of organizations held to be subversive