As you can see from my blog posts, there are many things to consider when it comes to warning letters, even aside from the question of whether the accusation actually made is justified. You should take a particularly close look when a so-called competition association issues a warning. These often generate a large part of their revenues by sending warnings to other competitors.
Here it is not only important to consider whether one should issue a cease-and-desist declaration at all (see this article), even if the accusation is justified, but one should also look very closely at whether the association was allowed to issue a warning at all.
The requirements for this are regulated in the UWG in Section 8 (3) No. 2. The warning is in fact only
associations with legal capacity for the promotion of commercial or independent professional interests, insofar as a considerable number of entrepreneurs belong to them who sell goods or services of the same or a related kind on the same market, if they are able, in particular according to their personnel, material and financial resources, to actually perform their statutory tasks of pursuing commercial or independent professional interests and insofar as the infringement affects the interests of their members;
Numerous court rulings have further specified these requirements; for example, the Karlsruhe Regional Court recently ruled, with reference to supreme court case law, that such a competition association must present its list of members in court proceedings without blackening. The submission of an anonymized list is not sufficient, even if the association presents conflicting confidentiality interests.
Since the plaintiff here refused to disclose its members, the case was dismissed. The requirements have become more and more restrictive in recent years, especially with regard to the question of whether the number of members is material. You can also read this article.