Now, plaintiffs are again bringing suit on the letter agreement, claiming essentially that their contractual rights remain enforceable, independent of any determination by the PSC with regard to price. A subsequent suit between the same parties when the evidence or essential facts remain the same is barred by the doctrine of res judicata. The applicability of res judicata is a question of law, which we review de novo. The grant or denial of a motion for summary disposition is reviewed under the same standard. An order granting summary disposition under the wrong subrule may be reviewed under the correct one.
Plaintiffs contend that various factual issues remain unresolved.
Virtually all these issues relate to defendant's failure to file the letter agreement and whether plaintiffs were entitled to rely on the provisions of that agreement. As the trial courts properly concluded, plaintiffs' claims with regard to the letter agreement were resolved, either expressly or by implication, by this Court in North Michigan , supra . Plaintiffs first claim that the PSC lacked jurisdiction to hear breach of contract claims. This Court has repeatedly held that the PSC has primary jurisdiction over the interpretation of gas purchase contracts. Moreover, this Court expressly considered and rejected North Michigan's arguments regarding the PSC's authority to resolve contractual claims in North Michigan , supra at 437.