יורה דעה קי״זYoreh De'ah 117

Se’if 1א׳

כָּל דָּבָר שֶׁאָסוּר מִן הַתּוֹרָה, אַף עַל פִּי שֶׁמֻּתָּר בַּהֲנָאָה, אִם הוּא דָּבָר הַמְיֻחָד לְמַאֲכָל, אָסוּר לַעֲשׂוֹת בּוֹ סְחוֹרָה, אוֹ לְהַלְווֹת עָלָיו (ת"ה סִימָן ר') וַאֲפִלּוּ לִקְנוֹתוֹ לְהַאֲכִילוֹ לְפוֹעֲלָיו עוֹבְדֵי כּוֹכָבִים אָסוּר (כָּךְ מַשְׁמָע מִבֵּית יוֹסֵף מֵהַגָהוֹת מַיְמוֹנִי פ"ח דְּמַאֲכָלוֹת אֲסוּרוֹת), חוּץ מִן הַחֵלֶב, שֶׁהֲרֵי נֶאֱמַר בּוֹ: יֵעָשֶׂה לְכָל מְלָאכָה (וַיִּקְרָא ז, כד). וְאִם נִזְדַּמְּנוּ לְצַיָּד חַיָּה וְעוֹף וְדָגִים טְמֵאִים, וְכֵן מִי שֶׁנִּזְדַּמְּנָה לוֹ נְבֵלָה וּטְרֵפָה בְּבֵיתוֹ, (טוּר), מֻתָּר לְמָכְרָם וּבִלְבַד שֶׁלֹּא יִתְכַּוֵּן לְכָךְ. הַגָּה: וְצָרִיךְ לְמָכְרָהּ מִיָּד, וְלֹא יַמְתִּין עַד שֶׁתְּהֵא שְׁמֵנָה אֶצְלוֹ (בֵּית יוֹסֵף בְּשֵׁם א"ח). וְכֵן מֻתָּר לִגְבּוֹת דְּבָרִים טְמֵאִים, בְּחוֹבוֹ, מִן הָעוֹבְדֵי כּוֹכָבִים, דְּהָוֵי כְּמַצִּיל מִיָּדָם (רַשְׁבָּ"א בִּתְשׁוּבָה). וְאָסוּר לִמְכֹּר לְעוֹבֵד כּוֹכָבִים נְבֵלָה בְּחֶזְקַת כְּשֵׁרָה (טוּר). וְעַיֵּן בְּחֹשֶׁן הַמִּשְׁפָּט סִימָן רכ"ח. וְכָל דָּבָר שֶׁאֵין אִסוּרוֹ אֶלָּא מִדִּבְרֵיהֶם, מֻתָּר לַעֲשׂוֹת בּוֹ סְחוֹרָה.

Not to engage in commerce with a forbidden item. Containing 1 paragraph. Anything that is specifically for eating and Biblically prohibited, even though it is not forbidden to derive benefit from it, is forbidden to do business in it. (Or to lend with it as collateral) (Terumat HaDeshen §200) (And even to purchase it to feed it to one’s idol worshiping workers is forbidden)(based on Hagahot Maimoniyot, Laws of Forbidden Foods ch. 8). Except for Biblically prohibited fats because the Torah says in regard to it: “it may be used for all kind of work." And if impure wild animals or birds or fish happened into the trap of a trapper (Additionally one into whose house happened a nevelah or treifah) he is permitted to sell them, assuming that he did not intend for them to come into his possession in the first place. Rema: And he needs to sell them immediately and not to wait until they become fat in his possession (Beit Yosef in the name of Orchot Chayyim). And it is also permitted to collect impure things from an idol worshipper for a debt because this is like rescuing [what is yours] from their possession (Rashba, responsa). It is forbidden to sell an idol worshipper nevelah claiming that it is kosher (See also Tur Choshen Mishpat Siman 228). And anything that is only prohibited rabbinically, it is permitted to use it for commerce.