May one own stocks in a food company or restaurant chain that sells Basar Bechalav [i.e. McDonalds]?
Owning stocks in a company which sells Basar Bechalav raises the question of whether the owning of stocks transgresses the prohibition against doing business with non-Kosher foods, and the prohibition against benefiting from it. Practically, it is debated amongst the Poskim as to the status of stocks. Some Poskim rule that owning stocks in a company is not considered ownership of the food of the company and hence one does not transgress doing business or benefiting upon owning the stocks. Other Poskim, however, rule that owning stocks of a company considers one a Halachic partner of ownership in all their assets, and it would hence be forbidden to own stocks in a Basar Bechalav company. Practically, each person is to consult with their Rav. According to all, the above dispute only applies if one is a limited share holder, or non-active party, it is however forbidden to own enough stock in a Basar Bechalav company to hold power rights within the company.
 See Michaber 117:1
 Igros Moshe E.H. 1:7 [permits if no decision-making ownership]; Cheishev Haeifod 1:82 in name of Tchebiner Rav based on Mahariy Levi 2:124
 Minchas Yitzchak 3:1; 7:26; Moadim Uzmanim 3:269; The Rebbe in Reshimos 161 is of the opinion that owning even a single stock considers one a partner, and hence seemingly, it would be prohibited to own stock in any Basar Bechalav company.