This halachah gives rise to the question concerning owning stock in non-kosher food chains, such as McDonald’s. By owning shares in the company, the shareholder is effective a partner in the trade of non-kosher products. Would this ‘passive trading’ also be included in the blanket enactment?
The question, we should note, is limited to companies that trade exclusively (or close to exclusively) in non-kosher foods. If the sale of non-kosher foods constitutes only part of the company’s trading—which is frequently the case, with the exception of abattoirs and the like—all authorities would agree that there is no prohibition in making an investment (see Pischei Teshuvah, YD 117:6). In fact, the prohibition of trading in prohibited foods applies solely to foods that are prohibited by the Torah. Thus, when a (significant) part of the company’s trading is involves rabbinically prohibited goods, it would be permitted to make an investment.
Concerning investing in McDonald’s or non-kosher slaughterhouses, Rabbi Chanoch Padwa (Cheishev Ha’eifod Vol. 3, sec. 44) adopted a strict position, ruling that it is prohibited to invest in a company that trades in (predominantly) non-kosher food. Although concerning shareholding in general he adopts a lenient position, maintaining that shareholding does not constitute halachic ownership of company assets, he writes that it is nevertheless constitutes a partnership in forbidden sales, and is therefore prohibited.