A warning letter sent to an infringer directing them to “cease and desist” from infringing intellectual property rights. Typical in trademark matters, it should be sent with caution in patent matters since it can provide the basis for bringing a declaratory judgment case. Moreover, in a number of countries, sending a warning letter without a proper legal basis may expose the sender to a legal claim for damages by the recipient or the person accused of infringement. Sometimes known as a letter of protest or in slang as a “nastygram.”