(a)     Any employee representing an exclusive representative in the negotiation of a collective bargaining agreement under this chapter shall be authorized official time for such purposes, including attendance at impasse proceeding, during the time the employee otherwise would be in a duty status. The number of employees for whom official time is authorized under this subsection shall not exceed the number of individuals designated as representing the agency for such purposes.

      (b)     Any activities performed by any employee relating to the internal business of a labor organization (including the solicitation of membership, elections of labor organization officials, and collection of dues) shall be performed during the time the employee is in a nonduty status.

      (c)     Except as provided in subsection (a) of this section, the Authority shall determine whether any employee participating for, or on behalf of, a labor organization in any phase of proceedings before the Authority shall be authorized official time for such purpose during the time the employee otherwise would be in a duty status.

      (d)     Except as provided in the preceding subsections of this section--

      (1)     any employee representing an exclusive representative, or

      (2)     in connection with any other matter covered by this chapter, any employee in an appropriate unit represented by an exclusive representative,

shall be granted official time in any amount the agency and the exclusive representative involved agree to be reasonable, necessary, and in the public interest.