This article is from the sci.lang.translation FAQ, by James Hester (firstname.lastname@example.org) with numerous contributions by others.
(I'm not a lawyer and neither are most of the people in the newsgroup, so
I make no claim to the accuracy of the statements below)
The legal position of a person posting non--payment information to the
net is unclear at the time of writing (July 1996), although it seems
reasonable to expect that laws against slander and malicious
interference would apply. One suggestion (Gabe Bokor) was to post a
message along the lines of "If you're considering doing business with
the XXX company, contact me for information that could be of interest
to you" although another poster (Steve Marzuola) thought that, if it
was illegal to publish a blacklist, then disguising the information in
this way would not provide protection. Some UK organisations happily
publish such lists or hints in their newsletters (Gerlinde Krug).