In Choshen Mishpat, does it discuss the halacha of giving preference to a Jew as opposed to a non-Jew in business transactions (buying from and selling to.) This is addressed by Rashi and in Torah Temima on the basis of Behar 25:14
This is discussed by a number of sources, though the halachah does not appear in Shulchan Aruch.
Please see sources below.
The primary source relating to this issue is teaching of the Sifra (Behar 3): “From where do we learn that when one sells one should sell specifically to one’s fellow? – For it says (Vayikra 25:14): ‘When you shall sell a sale to your fellow.’ And from where do we learn that when one buys one should buy specifically from one’s fellow? – For it says: ‘or buy from the hand of your fellow’” (the teaching is cited by Rashi on the verse).
The Rambam and the Shulchan Aruch do not mention this halachah. Yet, it is noted by the Rema – not in his glosses to Shluchan Aruch, but in his responsa (no.10).
The Rema discusses a case in which a non-Jewish publisher rivalled a Jewish scholar and sold the same work at a substantially cheaper price. Despite the difference in price, the Rema ruled (based on the halachah of the Sifra, together with three other reasons) that it was forbidden to buy the book from the non-Jewish publisher in favor of the Jewish one. The ruling is cited by several Poskim after him, and has still earlier sources in the Rashbatz (3:151) and the Chinuch(337).
Some relate to this halachah as a “mitzvah” and some as a full obligation. Concerning the amount of loss one should be prepared to incur, the Chafetz Chaim (Ahavas Chessed 5:5-7 and note 9) states as “simple” that it only applies to a small discrepancy, and not where there is a great difference in prices. This is not mentioned by other authorities.
We have discussed the principles at greater length in a previous article on the subject.