Chullin 106a: Not washing before a meal caused a Jew to eat pork. Rashi: There was a Jew who owned a restaurant serving kosher meat to Jews and neveilah meat to gentiles. Once a Jew came and did not wash his hands before eating, so the restaurant owner thought he was a gentile and served him pork.
חולין קו ע”א: מים הראשונים ־ האכילו בשר חזיר. רש”י: שהיה חנוני ישראל מוכר בשר שחוטה לישראל ומבשל ומאכילם וכשהעובד כוכבים בא בחנותו מאכילו נבלות ובא יהודי אחד לאכול ולא נטל ידיו וכסבור זה שעובד כוכבים הוא והאכילו בשר חזיר.
Someone once asked Rav Ovadiah Yosef: “If I can’t find another job, may I work in a treif restaurant, provided that I will not be cooking meat and milk together?”
The question hinges on whether there is any Rabbinic prohibition on working with treife food lest he come to eat it.
Rav Ovadiah quotes the Kesef Mishnah (Tumas Mes 1:2) who says that the reason why it’s forbidden to cook meat and milk together is out of fear that one might come to eat it. This goes into the category of gezeiros made by the Torah itself – similar to yichud. Yet, cooking a non-kosher animal’s meat with milk is allowed (Yoreh Deah 87:3). The prohibition is only on kosher meat (at least a kosher animal) and milk, because people are used to eating it each separately and may accidentally come to eat them together. This shows that there is no prohibition on working with treife food.
The Rashba (3:223) does say that the prohibition on doing business with forbidden food is because one might come to eat it. If so, “doing business” would include even an employee who does not own the business, because he too might come to eat. However, this is only the Rashba, who holds that doing business is a Rabbinic prohibition. According to most Rishonim, it is a D’oraisa, so “one might come to eat it” may not be the reason.
The Gemara in Chullin 106a seems to address this exact question. The Gemara quotes a saying, “Not washing before a meal caused a Jew to eat pork,” and Rashi tells the story of a Jew who owned a restaurant serving kosher meat to Jews and neveilah meat to gentiles. Once a Jew came and did not wash his hands before eating, so he thought the proprietor mistook him for a gentile and served him pork. The Maharsha asks: why did Rashi begin by saying that this Jew served neveilah to gentiles, and then end by saying that he served pork to this customer? He explains that the Jew usually sold neveilah meat – not pork – because one may not deliberately do business with non-kosher, so he sold only the neveilah that resulted from mistakes in shechitah. It was only this time that he happened to have some pork on hand. So we see that the Maharsha was assuming that this proprietor was an observant Jew. If so, we see that it’s okay for a Jew to cook and serve non-kosher food to gentiles.
However, the Beis Yosef (end of 117) argues that the restaurant owner may have been a non-observant Jew, and besides, this story is no proof because, as the Midrash (Bamidbar 20:21) says, the story took place during the period of Greek persecution. The Jew sold pork deliberately in order to hide his Jewish identity, and the hand-washing was a secret cue for the Jews to show him they were Jewish, so that he should serve them kosher meat.
In the end, Rav Ovadiah paskened that this unemployed person should try his hardest to find a different job, in order to follow the stricter opinion. But if there was no other way, he could rely on the Maharsha and take the job in the treif restaurant.