Under Maryland’s jurisprudence of at-will employment, any employer or employee can in general end the employment without notice, excuse, severance, cause or explanation. In most cases, it is perfectly lawful in Maryland for an employer to fire a worker and instruct the worker to leave the premises under pain of arrest, just as it is perfectly lawful in most cases for a maitre’d at a most expensive restaurant in town to quit his or her job on a Friday night Valentine’s Day with a crowded restaurant and the mayor and half a dozen television cameras walking in. Both are “jerk moves”; both are in general lawful in Maryland.
Under Maryland law only, there would be no apparent impediment against firing a worker for violating a company rule against discussing salaries, wages or other working conditions with other workers.
The U.S. National Labor Relations Act prohibits in many cases (not all) retaliation against workers for discussing or complaining to other workers about wages and working conditions. While most of the provisions of the NLRA govern primarily formal collective bargaining units and employers, the Act is broad enough to cover some communications between co-workers about work conditions even if a union or other bargaining unit does not exist or is not part of the discussion. The National Labor Relations Board has reviewed cases involving discussions on Facebook, for example, between employees of pay and working conditions, and has in some cases (not all) found those discussions to be protected under the NLRA.
Not all employers and not all employees are covered under the NLRA. Employers who operate in federal enclaves (notably the District of Columbia) and employers about certain gross revenue figures per year in most industries are covered; law firms and legal assistance agencies, for example, are covered if their gross revenue is over $250,000 per annum. Some employees are not covered such as management and supervisory employees and some others.
If you have been fired for talking about your pay with other workers you may (or may not) have a remedy before the NLRB – even if your shop is not a union shop. You should consult legal counsel.