In Kellogg Co. v. NLRB, 457 F.2d 519, 525 (6th Cir. 1972), we stated that the employees' right to honor another's picketline may only be waived through "clear and unmistakable language."
In Gary Hobart, not only was the contract lacking any acknowledgement of the industrial necessity to avoid work stoppages, but the no-strike clause and the grievance and arbitration procedures of the contract were fundamentally related.
Holding one bargaining unit of the union violated the no-strike clause of its CBA when its members refused to cross the picket line of another bargaining unit
In Amcar Division ACF Industries, Inc. v. NLRB, 641 F.2d 561 (8th Cir. 1981), the Eighth Circuit found that employees may waive their right to engage in sympathy strikes.