The real-estate lobby called the move “an unprecedented breach.” But there’s a much larger concern for legacy brokers than the novelty of the about-face.

Real estate brokers and their supporting organizations function as a cartel that stifles competition and protects high commission rates, the Consumer Federation of America charged in a report Monday.

The son of a wealthy real estate magnate from Guadalajara, Mexico, admitted Wednesday afternoon to laundering drug cartel money in San Antonio land deals. Alejandro Sánchez Garza, 43, pleaded ...