The broker allegedly supplied unwitting customers with out-of-date Thomson Local data for direct marketing purposes, breaching the company's copyright and database rights.
Gary Brown, the product and marketing director at Thomson Local, said: "The company concerned obtained and sold Thomson Local data without authorisation; this is completely unacceptable. Our data is an extremely valuable commodity and we will protect its integrity fiercely."
He added: "We have a duty not only to protect this quality, but our existing licensees who have recognised its value and obtained it through the correct process.
Brown warned: "Every business that uses data has a legal duty to ensure that they are using it in the correct manner and not breaching any copyright."
Thomson Local has been operating for over 25 years and offers its directory service in both print and online following the launch of in 2003.
It delivers 174 editions of its directory free of charge to over 22 million UK homes and businesses.