Most employees in California, and across the country, are considered "at-will" employees. This entitles their employer to terminate their employment at any time, and for any reason. An employer is typically protected from liability in such situations, unless they are found to have violated an employee's rights or protections in doing so.
An employee can be classified as an at-will employee through contract, an employer's words or an employer's actions toward the employee. Although an employee is considered at-will by their employer, they are still entitled to certain rights. Among them is protection from discrimination as a result of their membership in a protected class, such as gender, race, disability or religion. Any employee who is treated improperly or unfairly by their employer as a result of their inclusion in such a class may be able to pursue legal action against their employer to assert their rights. Additionally, if an employee reports a compliance concern to an outside agency regarding their employer's activities and the employer retaliates against the employee as a result, including termination from employment, the employee may be entitled to assert their rights against such retaliation.
Essentially, at-will employees are afforded protection from a wrongful termination. Such a termination can occur as a result of the circumstances above, or if an employer is in violation of the terms of an employment contract by getting rid of an employee. Some employers have gone so far as to request that their employees sign at-will employment agreements, even though employees are typically not required to sign them, and they are not an indication that an employee will be terminated without notice.
Employees who are subject to a wrongful termination may be afforded various remedies, including financial compensation, job reinstatement, promotion and injunctive relief.
Source: FindLaw, "At-Will Employee FAQ's," accessed on June 14, 2015