At-will employment varies by state, so CapitalistCartr's comment above is true in many states[1]. For example, in Georgia, your employment can be terminated for no reason at all at any time (as long as it is not for a protected reason, i.e. firing because of the employee's race, religion or sexuality).

edit: changed Florida to Georgia because Florida specifically appears to have at least some exceptions to this[2]. In Georgia it seems even if your employer is doing something illegal and you report it, they can legally fire you in retaliation.

[1] https://en.wikipedia.org/wiki/At-will_employment#By_state

[2] http://www.leg.state.fl.us/statutes/index.cfm?App_mode=Displ...