(dissenting).
The majority interprets section 179.65(5) to allow minority dues checkoff when the agreement between the school district and the exclusive representative so provides. The issue then becomes whether the exclusive representative has so agreed in this case. The majority does not undertake to answer this question.
Several factors demonstrate that the exclusive representative has agreed to permit minority dues checkoff. First, its contract with the school district has never prohibited this practice. If the contract was intended to prohibit minority dues checkoff, then it should have so provided. The fact that the contract never prohibited this practice becomes especially important in view of the fact that minority dues checkoff was permitted by the school district until August 20, 1973. Although the practice stopped at that time, no new language prohibiting minority dues checkoff was added to the contract. The 1973 amendment to section 179.-65(5) went into effect on May 25, 1973.1 For three months, the school district allowed minority dues checkoff under the new statute, and the exclusive representative acquiesced in the practice. If the contract with the school district permitted this practice in 1973 after the statute was amended, then the same contract should permit the same practice today. See Restatement (Second) of Contracts § 249 (Tent.Draft No. 6, 1971) (prior conduct of parties supplements and is used for interpreting agreement).
Second, the practice complained of in this case is one that is followed in many other school districts throughout the state. It is a custom in the profession and, because it is not prohibited by the contract, it becomes a term of the exclusive representative’s contract with the school district. See id. § 247 (agreements are supplemented by customary practice with respect to other agreements of the same type).
Finally, there is another factor that shows the parties did not intend their contract to prohibit minority dues checkoff. An affiliate of one of the plaintiffs in this case was involved in a 1974 arbitration proceeding that interpreted section 179.65(5) to give school districts the discretion to permit *331minority dues checkoff. Although this court gives no deference to an arbitrator’s interpretation of a statute, the arbitrator’s decision did give plaintiffs reason to know that section 179.65(5) might not prohibit minority dues checkoff. Yet the contract was never amended to prohibit the practice. This also shows long-term acquiescence; by the plaintiffs and demonstrates that the parties intended their contract to permit minority dues checkoff.
The prior conduct of the parties and the customs of the profession show quite clearly that the contract in this case allows minority dues checkoff. The majority decision acknowledges that the parties can agree to permit this practice, yet it does not decide whether such an agreement has been made. Because the facts demonstrate such an agreement, however, the trial court’s decision should be reversed.
SCOTT, Justice(dissenting).
I agree with the dissent of YETKA, J.
. See Act of May 24, 1973, ch. 635, § 38, 1973 Minn.Laws 1526, 1541 (effective date provision).