From the described case in the question, it is clear that Frank believes in doctrine called at-will employment or employment at-will.
At-will employment is a U.S term used for a condition where an employee can be fired at anytime and without any warning as long as the reason isn’t illegal by law.
This type of doctrine is no longer the main doctrine used in most U.S states by the 20th century, but it was commonplace during the late 19th century.