(a) A petition for review must be filed within fifteen (15) days after the date of service of either:

(1) An agency's written allegation that the exclusive representative's proposal is not within the duty to bargain, or

(2) An agency head's disapproval of a provision.

(b) If the agency has not served a written allegation on the exclusive representative within ten (10) days after the agency's principal bargaining representative has received a written request for such allegation, as provided in §2424.11(a), then the petition may be filed at any time.