Register.com has sued Domain Registry of America, claiming the company illegally lured away thousands of customers by tricking them into transferring their domains. In the complaint, filed last month in federal court in New York, Register.com claims Domain Registry of America mined its public customer database and then sent promotional mailings that appeared to be affiliated with Register.com, asking customers to renew their Web addresses.

Register.com customers were then directed to a Domain Registry of America site, the complaint says. Register.com claims the company's materials make "liberal use of Register.com's name and marks and are intentionally designed to give the false impression that defendants are affiliated with, part of, or acting on behalf of Register.com itself."

Domain Registry did not immediately respond to requests for comment.

As more companies have entered the market for registering domain names, registrars have adopted increasingly aggressive tactics to land new business. However, courts and federal regulators have frowned upon attempts to lure customers by sending them bogus messages.

Domain giant VeriSign recently signed a federal order sending false notices that tell customers of rival registrars their domain names will soon expire. Rival GoDaddy had sued VeriSign, seeking to halt the practice. BulkRegister brought a similar case, winning an injunction prohibiting the tactic.