It shall be unlawful for any operator of a milk processing? plant or any milk distributor, required to make reports under this Article, or their affiliates or subsidiaries, to sell, use, transfer, or distribute any milk in a classification higher than the classification in which it was purchased, except in an emergency declared and approved in writing by the local board of health having supervision of operators and distributors on such market for a period? of two weeks, and such period may be extended if, in the opinion of the local board of health, an emergency still exists at the end of such two weeks’ period. (1941, c. 162, s. 4.)