(1) One of the parties to a bilateral contract may refuse performance of his or her own obligation until the other party tenders performance of his or her obligation; provided, this shall not apply where the obligation of the other party is not due.
(2) If one of the parties to a contract is bound to tender performance of his own obligation first to the other party, and if there is any significant cause existing by which the other party's performance becomes difficult, the body of the preceding paragraph shall apply.