The Chief Rabbinate has allowed Tnuva, the nation's largest dairy, to mislead consumers by not specifying that products marked kosher contain derivatives considered by some to be non-kosher, according to a petition presented to the Supreme Court. The petition comes on the eve of Shavuot as dairies step up their marketing efforts to take advantage of the Jewish custom of eating milk products in honor of the holiday. The Movement for Fair Government's Mordechai Eisenberg and attorney Nechama Tzivin argue in their petition that Tnuva rabbi Ze'ev Weitman permits the use of milk proteins and ingredients derived from halav nochri - milk that was milked by a gentile or without Jewish supervision - without specifying this on the product's package. Eisenberg and Tzivin also argue that the Chief Rabbinate has failed to enforce its own directives requiring all products containing such milk to be specifically marked as such. Halav nochri is prohibited by many rabbis for fear it might contain milk from a non-kosher animal. But some rabbis, most notably the late Rabbi Moshe Feinstein, a prominent leader of Orthodox Jews in the US, have argued that such milk is permitted since contemporary health standards, enforced through the imposing of heavy fines, ensure cow's milk remains pure. Many Orthodox Jews, relying on Feinstein's opinion, do eat and drink halav nochri products. Tnuva was singled out in the petition because it is the only dairy that openly notifies its customers both on its Internet site and in newspaper ads that products marked kosher but not mehadrin (stringently kosher) contain halav nochri derivatives. However, senior kosher supervision sources told The Jerusalem Post that Tnuva is not the only dairy that includes such milk in its regular kosher products. Strauss, Nestle and Ma'adanot do as well, said the sources, because the rabbinate does not senforce its own directives properly. Tnuva's Weitman said in response to the petition that the rabbinate had never obligated Tnuva to mark its products. But, he added, if required to, he would agree to mark all kosher products with a label, reading "contains halav nochri." However, he argued that marking such products would give the impression that these products are somehow less kosher. "In reality, these products might be more kosher because we at Tnuva are more stringent regarding a host of other issues that are even more serious than halav nochri," said Weitman. Rabbi Ya'acov Sabag, head of the rabbinate's kashrut department, could not be reached. However, in a letter to the Movement for Fairness in Government dated March 2005, Sabag wrote that the rabbinate was doing its best to enforce its directives. "To our dismay there are several factories that did not comply with our requests to mark products that contain halav nochriand therefore are not providing proper service to the consumer," he wrote.