Except so far as a seller may have assumed a greater obligation and subject to the preceding section on substituted performance:

(a) Delay in delivery or nondelivery in whole or in part by a seller who complies with subsections (b) and (c) of this section is not a breach of his or her duty under a contract for sale if performance as agreed has been made impracticable by the occurrence of a contingency the nonoccurrence of which was a basic assumption on which the contract was made or by compliance in good faith with any applicable foreign or domestic governmental regulation or order whether or not it later proves to be invalid.

(b) Where the causes mentioned in subsection (a) of this section affect only a part of the seller's capacity to perform, he or she must allocate production and deliveries among his or her customers but may at his or her option include regular customers not then under contract as well as his or her own requirements for further manufacture. He or she may so allocate in any manner which is fair and reasonable.

(c) The seller must notify the buyer seasonably that there will be delay or nondelivery and, when allocation is required under subsection (b) of this section, of the estimated quota thus made available for the buyer.