Actually, in theory, it CAN be stopped. One of the requirements for obtaining/granting a "hecksher" (Rabbinical certification of kosher compliance) is that the store not infringe on anyone else's livelihood-- Even if every product carried in the store is kosher. It sounds like protectionism, and it is, but it's one of the reasons that there are so few kosher places in the Washington, DC area, where the local Va'ad Hakashruth (the Board of Kosher-overseeing Rabbis) is very protecive of its current providers. If the rabbinical establishment of Chicago denies the Jewel store its certification, the store will suffer. It can get certified by a different, out-of-town board, but lots of people will boycott it because the hecksher isn't good enough.

--Charlie Baum (embarrassed to share this bit of dirty linen about the way kosher certification actually works)