IANAL. In the US. You can argue that there's an implicit assumption that you will not work on vacation in the employment agreement. Most of the US states are at

IANAL. In the US. You can argue that there's an implicit assumption that you will not work on vacation in the employment agreement. Most of the US states are at will states, i.e. a person can be fired for no reason at all, but having a wrong reason, especially when documented in a termination letter, might be a cause for litigation.