The targets of the suit, which was filed in federal court, are the Creig Northrop Long and Foster Real Estate and the Lakeview Title Company.
Patrick and Christine Baehr, of Howard County, claim that Lakeview paid about $500,000 in kickbacks to the Northrop team over more than ten years in a deal to send homebuyers to the title company.
If true, that would violate federal laws for real estate transactions.
The lawsuit is seeking more than $11 million.
Lawyers for the companies insist there was no wrongdoing and intend to ask for the case to be dismissed
The suit, which could become class action, stems from a 2011 lawsuit that a judge tossed out because it was filed after a deadline for doing so.