In Litton Financial Printing Div. v. NLRB (1991) 501 U.S. 190, the Supreme Court discussed the principle that an employer cannot, after expiration of a collective bargaining agreement and without bargaining to impasse, effect a unilateral change of an existing term or condition of employment. ( NLRB, 501 U.S. at p. 198.) Most terms and conditions of employment are subject to this prohibition on unilateral changes, which derives from the statutory requirement to bargain in good faith. ( Id. at p. 203.) However, the court identified three exceptions to the prohibition on unilateral changes. The exceptions are union security and dues checkoff provisions, no-strike clauses, and arbitration clauses. ( Id. at pp. 199-200.) These provisions do not continue in effect during bargaining without the consent of both parties. In each case, the basis for requiring consent of both employer and union to the continuation of the provision after the expiration of the collective bargaining agreement is statutory. For example, no-strike clauses are excluded from the unilateral change doctrine because employees have a statutory right to strike. ( Id. at p. 199.)