While Maryland does not have any officially approved right-to-work laws, there is a section within their Labor and Employment code that outlines employee protections relating to labor organizations.
Essentially, employers cannot coerce employees to join or stay in a labor organization, or force employees to leave their job or position due to their involvement (or desire to be involved) in a labor organization.
So, although there is no explicit right-to-work law, there is still a level of safeguarding against manipulation through labor union membership.