(a)      Except as otherwise provided in this subtitle, the Board shall conduct an election for an exclusive representative of a bargaining unit if:

            (1)      a valid petition is filed in accordance with § 3-402 of this subtitle; and

            (2)      the bargaining unit involved in the petition is determined to be an appropriate bargaining unit under § 3-403 of this subtitle.

      (b)      The Board may not conduct an election for an exclusive representative of a bargaining unit if the Board has conducted an election or certified an exclusive representative for that bargaining unit within the preceding 2 years.