Whether parol evidence of bargaining history is admissible in a court's determination of arbitrability is a problem arising out of the United States Supreme Court's 1960 decisions in the Steelworkers Trilogy. The Court there emphasized the national labor policy favoring arbitration as the best means of resolving labor disputes. Citing its earlier Lincoln Mills decision interpreting section 301(a) of the Labor Management Relations Act, the Court stated that, in enacting section 301, Congress assigned the question of the jurisdiction of an arbitrator to the courts in the absence of an agreement by the parties specifically assigning the question to an arbitrator. While rejecting a judicial criterion of ordering arbitration of only those grievances as to which there is a bona fide dispute, the Court specifically avoided "the prescription of inflexible rules," stating rather that the lower courts were to be guided by "considerations of the milieu in which the clause is negotiated and of the national labor policy." The parol evidence rule, as often applied, would seem to be the type of inflexible rule that the Court would wish to avoid.
Michigan Law Review,
Admissibility of Parol Evidence in Judicial Determinations of Arbitrability,
Mich. L. Rev.
Available at: https://repository.law.umich.edu/mlr/vol63/iss7/8