Employment law in the U.S. has traditionally been governed by the common law rule of "at-will employment," meaning that an employment relationship could be terminated by either party at any time for any reason or without a reason. This is still true today in most states. However, starting in 1941, a series of laws prohibited certain discriminatory firings. That is, in most states, absent an express contractual provision to the contrary, an employer can still fire an employee for no or any reason, as long as it isn't an illegal reason (which includes a violation of public policy). http://en.wikipedia.org/wiki/United_States_labor_law and http://en.wikipedia.org/wiki/At-will_employment
“While most people in the USA do not seem to care about practices in other countries, several law review articles have noted that the USA is alone among the industrialized nations of the world in providing no protection against wrongful termination of employment.” http://www.justlawlinks.com/PRACTICE/ctlabor.htm
Take heed. High level CEO’s and public managers (school superintendents, fire chiefs, city managers, top hospital administrators, etc.) have tightly-written contracts that either abolish “at-will” common law for their particular employment, and pay high stock dividends or “buy-outs” when the employer wants to release that person prior to the contracts duration language.
Also lament, the United States is the only industrialized country that has no mandatory sick leave (even with Swine flu upon us), no mandatory vacation law, and the longest work week and shortest average vacation times taken of the industrialized world. Yet, we claim to be “the best country in the world to live in.” Love it or change it. California Healthy Workplace Advocates vote for change.