When can you terminate someone’s employment, and can it be for any reason, at any time? When can you not terminate someone’s employment?
Please reference employment at will, wrongful discharge, just cause.
The terms of when an employer may terminate an employee's job vary depending upon the national and state requirement. At present the US is the only major national power in the world that does not require the employer to prove "good cause" and act in accord with termination standards (West's Encyclopedia of American Law).
To put it the other way, the US is the only nation with "at will" termination in which either the employee or the employer may end a work agreement at any time for any reason.
Other nations require good cause, fair notice, redundancy and final pay regulations be met. Australia is an example of a nation where these requirements are part of the legal employment system.