Applying Non-Employment Laws in the Workplace
Working on an employer's premises and time justifies a modification of the civil laws that protect all of us from being injured or violated by the acts/omissions of another. While most civil laws still apply in the workplace, they are diluted and/or construed in deference to the prerogative or an employer to control the conduct of its employees; and because employer's are often responsible for the welfare of (in a fiduciary role as to) employees in the workplace.
For example, an employer can defame an employee only by abusing the conditional privilege of being able to discuss the employee among management. As long as the discussion stays within the managerial "chain of command," it is nearly impossible to hold an employer accountable for defamation.
Even constitutional rights are subject to dilution. We all enjoy a right to be free from state intrusion on our First Amendment right to privacy. However, to the extent privacy rights are implicated (as for state and municipal employees), employees have a lower expectation of privacy, and therefore a lower level of protection against intrusions on privacy. For example, the use of e-mail sent/receive/stored on an employer's computer system becomes the property of the employer, and subject to the employer's review, virtually at will.
As a very broad rule of thumb, employees do not generally lose the rights and protections of the civil laws in the workplace - but employers are generally able to benefit from broader defenses to alleged violations of those laws.