In any legal action in which a municipal policemen's or firemen's pension and relief fund, or the fund's board of trustees, employee or administrator, is named as a party, the plaintiff or petitioner shall serve a copy of the complaint or petition upon the oversight board by certified mail, return receipt requested, within seven days of filing the legal action. Until proof of service is filed with the clerk of the court in which the action was filed, and for sixty days after the filing of the proof of service, no order may be entered by the court that directly or indirectly requires the expenditure or other disposition of pension funds or that determines the eligibility or entitlement of any member to any pension benefit payable from the pension and relief fund: Provided, That the court may enter such temporary or interim orders as may be needed to preserve and protect the assets of the fund. In any legal action involving a municipal policemen's or firemen's pension and relief fund the oversight board is entitled to intervene for the purpose of preserving the security or fiscal integrity of the pension fund.