Swearing fidelity to a king was a common practice in monarchies, but few today know that there was actually a point in U.S. history when swearing an oath against a king was mandatory. In Maryland, this document was called an Oath of Fidelity or Oath of Allegiance.
Oaths of Fidelity
"An Act for the Better Security of Government" was a Maryland law signed in 1777 which required all free men 18 and up to sign an Oath of Fidelity. This oath required the signatory to renounce the English monarch -- at the time, King George III -- and swear allegiance to the revolutionary government of Maryland. The penalties for not signing were harsh economic sanctions. Those who didn't sign were made to pay triple property tax and were not allowed to operate many types of businesses or practice certain professions. The Maryland Historical Society maintains records of those who signed these oaths.