Section 15. The attorney general may at the request of the board, maintain and prosecute an action against a trustee or plan administrator subject to this chapter for the purpose of obtaining an injunction restraining such persons from doing any act in violation of this chapter. If the court finds that a defendant is threatening or is likely to do any act in violation of this chapter, and that such violation will cause irreparable injury to the interests of the citizens of the commonwealth or the beneficiaries of the trust or fund involved or any employer contributing to such fund, the court may grant an injunction restraining such violation. The court may, on motion and affidavits, grant a preliminary injunction and in interlocutory injunction, upon such terms as may be just, but the citizens of the commonwealth shall not be required to give security before the issuance of any such injunction.