Objections to the petition may be filed by a party within fifteen (15) days of the filing of the petition. If objections to the petition are filed, the administrative law judge shall then determine whether petitioners have the requisite interest to be a party in the
section 521 proceeding, as defined in
paragraph (b) of this section, and shall permit or deny participation accordingly. Where persons with common interest file petitions to participate as parties in a
section 521 proceeding, the administrative law judge may request all such petitioners to designate a single representative, or the administrative law judge may designate one or more of the petitioners to represent the others. The administrative law judge shall give each such petitioner, as well as the parties, written notice of the decision on his or her petition. For each petition granted, the administrative law judge shall provide a brief statement of the basis of the decision. If the petition is denied, he or she shall briefly state the grounds for denial and may consider whether to treat the petition as a request for participation as amicus curiae.