Whenever a district court has issued an order under section
178 of this title enjoining acts or practices which imperil or threaten to imperil the national health or safety, it shall be the duty of the parties to the labor dispute giving rise to such order to make every effort to adjust and settle their differences, with the assistance of the Service created by this chapter. Neither party shall be under any duty to accept, in whole or in part, any proposal of settlement made by the Service.