If the Contracting Officer notifies the Contractor in writing that a strike or picketing—(a) Is directed at the Contractor or subcontractor or any employee of either; and (b) Impedes or threatens to impede access by any person to a DOT facility where the site of the work is located, the Contractor shall take all appropriate action to end such strike or picketing, including, if necessary, the filing of a charge of unfair labor practice with the National Labor Relations Board or the use of other available judicial or administrative remedies.