From: Rabbi Moshe Sofer
To: Unknown recipient
The Chasam Sofer analyzes the four categories of commercial competition (hasagas gevul) established by the Maharshal and concludes that rabbinical bans protecting publishers from competitors reprinting their seforim are well-grounded in halachah. Reprinting another's sefer combines multiple levels of prohibition, and since publishing is sacred work, permitting competition would reduce Torah literature. He validates the long-standing custom of issuing such protective bans.
Source: Shu"t Chasam Sofer CM §79