"National banks--huge companies that already enjoy the advantages of a federal charter--will dominate real estate," NAR president-elect Al Mansell says, describing what NAR believes will be the inevitable effects of the OCC rule. "Costs will rise. Service will decline. Competition in real estate will go the way of competition in banking itself."

With the study and additional convincing evidence in tow, 7,500 realtors in town for the industry's Midyear Legislative Meetings & Trade Expo are descending upon the halls of Congress to convince members to give a second look at the OCC rule and other legislative measures that give banks the upper hand.

"Our immediate goal is to get Congress to look at the rule and the process of how it came about," NAR's Steve Cook tells GlobeSt.com. "We want Congress to play a more aggressive role in looking at laws that favor federally chartered banks over consumers, other lenders, and real estate service providers."