Q: I obtained access to the customer base of my competitor. Can I run a telemarketing campaign aimed directly at his clients?

A: We mentioned last week that it is usually not possible to restrain someone from opening a competing store, since each store operates independently. However, it is problematic to target another person’s client base. Since the person invested effort and resources to establish this client base and has specific expectations to maintain their business, such marketing encroaches on his rights (Tosfos Kiddushin 59a).

Established clients are known in halacha as “ma’arufya.” The Rama cites two opinions and practices as to whether a person can restrict others from encroaching upon his established clients and dealing with them (C.M. 156:5). This restriction applies both to non-Jewish clients and, in a more significant way, to Jewish clients.

However, if you open a competing store and advertise publicly, you can serve your competitor’s clients who come of their own accord (Chasam Sofer C.M. #175). It is also permitted for you to provide promotional incentives, discounts and bonuses, since the other store can do the same (C.M. 228:18).