By Mike Scarcella

Oct 7 (Reuters) - Mortgage software provider Optimal Blue and nearly 30 major lenders including Rocket Mortgage, CrossCountry Mortgage and United Wholesale Mortgage have been accused in a federal lawsuit of conspiring to inflate residential mortgage fees for millions of U.S. homebuyers.

The proposed class action was filed on Monday in Nashville, Tennessee, by homeowners in Tennessee, Minnesota, Delaware and Rhode Island who claim the lenders used Optimal Blue’s pricing software to share non-public data on interest rates and fees, allowing them to coordinate pricing in violation of federal antitrust law.

The lawsuit claims the data-sharing scheme drove up mortgage costs nationwide and "transformed the American dream of homeownership into a financial nightmare."

Optimal Blue declined to comment, as did defendants United Wholesale Mortgage, Bank of America BAC.N and Wells Fargo WFC.N. Defendants including Rocket Mortgage RKT.N, CrossCountry Mortgage and JPMorgan Chase JPM.N did not immediately respond to requests for comment.

Attorney Robin van der Meulen, representing the homeowner plaintiffs, in a statement said they looked forward to "holding accountable unfair competitors and unfair competition, no matter the mechanism."

The lawsuit describes Plano, Texas-based Optimal Blue as "the dominant market intelligence and pricing software provider in the U.S. mortgage industry."

Lenders pay for subscriptions to access its business analytics tools, which allegedly have allowed them to monitor competitors’ pricing and adjust their own rates.

The lawsuit said Optimal Blue's tools include "daily, non-public, real-time, loan-level data dissected at the local level" and are used to price more than one-third of all mortgages nationwide.

The proposed class includes borrowers nationwide who obtained residential mortgages priced using Optimal Blue's tools between October 2021 and the present.

The plaintiffs said they are seeking unspecified monetary damages and a court order to stop the alleged price-fixing scheme involving Optimal Blue and the mortgage lenders.

The case is Angel D. Mendez et al v. Optimal Blue LLC et al, U.S. District Court for the Middle District of Tennessee, No. 3:25-cv-01140.

For plaintiffs: Robin van der Meulen, Carmen Medici and Patrick McGahan of Scott + Scott Attorneys at Law, and Brian Clark of Lockridge Grindal Nauen

For defendants: No appearances yet

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(Reporting by Mike Scarcella)