The National Labor Relations Board (NLRB) has ruled that companies may ban employees from sending personal email messages, or from sending messages that solicit or proselytize for outside organizations (including union-related messages), without violating the National Labor Relations Act.

In this case, The Guard Publishing Company (.pdf), a divided NLRB also changed the test for determining whether an employer has enforced its policies in a manner that discriminates against union-related activities. The former rule was that an employer that allows employees to use its equipment or other resources for non-work purposes may not discipline employees for using those resources for union-related purposes. The new rule is that an employer may make any number of distinctions -- for example, allowing charitable solicitations while prohibiting solicitations for other organizations, allowing personal messages while prohibiting messages sent on behalf of an organization, and so on -- without violating the law, as long as it doesn't explicitly prohibit only those activities that relate to union issues.