Maryland Code, Natural Resources § 1-503

(a) The following persons have standing to bring and maintain an action provided for in this section in the courts of equity of this State:

(b) Any person given standing by subsection (a) of this section may bring and maintain an action for mandamus or equitable relief, including declaratory relief against any officer or agency of the State or political subdivision for failure on the part of the officer or agency of the State or political subdivision to perform a nondiscretionary ministerial duty imposed upon them under an environmental statute, ordinance, rule, regulation, or order, or for their failure to enforce an applicable environmental quality standard for the protection of the air, water, or other natural resources of the State, as expressed in a statute, ordinance, rule, regulation, or order of the State, or any political subdivision upon the request of the defendant, the court in its discretion may join as a party defendant any person against whom the plaintiff is requesting that governmental action be taken following notice to that person and if the court determines that the joinder would serve the interests of justice.