Section 2--615. Excuse by Failure of Presupposed Conditions

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 non-delivery in whole or in part by a  seller
  who  complies  with  paragraphs  (b) and (c) is not a breach of his duty
  under a contract for  sale  if  performance  as  agreed  has  been  made
  impracticable  by  the occurrence of a contingency the non-occurrence 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 paragraph (a) affect only a part of
  the seller's capacity  to  perform,  he  must  allocate  production  and
  deliveries  among  his  customers  but may at his option include regular
  customers not then under contract as well as his  own  requirements  for
  further  manufacture. He 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  non-delivery and, when allocation is required under paragraph
  (b), of the estimated quota thus made available for the buyer.