In its complaint, the Department alleges that NARs policy restrains competition by requiring NAR-affiliated MLSs to adopt rules that will allow brokers to withhold their clients listings from other brokers websites by means of an opt out. In essence, NARs policy enables traditional brokers to block their competitors customers from having full on-line access to all of the MLSs listings. When exercised, the opt-out provision prevents web-based brokers from providing all MLS listings that respond to a customers search, effectively inhibiting the new technology, the Department said.

The NAR in August 2005 rescinded its 2003 Web policy allowing traditional real-estate agents to selectively opt out of sharing listings with Web-base brokers, but the modified policy still prohibited any broker participating in a multiple listing service (MLS) from sharing the listings online without the permission of the listing broker. The NAR controls most of the U.S. MLSes, which are joint ventures offered by competing brokers, according to court documents.

"This provision would prevent a VOW broker from providing over the Internet the same [listing] information that can be provided in person, or through any non-Internet technology, without restriction," wrote Judge Mark Filip, of the U.S. District Court of the Northern District of Illinois, in a decision released by the DOJ Tuesday.

A state-imposed rule that defined VOWs as advertising could enable traditional brokers to block the customers of their VOW-operating competitors from using the competitor's website to review the same set of listings that traditional brokers deliver to their customers by other means.

"The proposed amendments stifle competition at the expense of home buyers and sellers in New Mexico," said J. Bruce McDonald, Deputy Assistant Attorney General of the Department of Justice's Antitrust Division. "Consumer choice should not be restricted by 'one size fits all' regulation."