Notwithstanding any other provision hereof, the Contractor is responsible for delays arising out of labor disputes, including but not limited to strikes, if such strikes are reasonably avoidable. A delay caused by a strike or by picketing which constitutes an unfair labor practice is not excusable unless the Contractor takes all reasonable and appropriate action to end such a strike or picketing, such as the filing of a charge with the National Labor Relations Board, the use of other available Government procedures, and the use of private boards or organizations for the settlement of disputes.