A dispute that threatens to derail a huge housing development planned in Dorchester has burst into public view.

Copper Mill filed a lawsuit against POB Capital and Pactolus Private Wealth Management, alleging they engaged in fraud during their negotiations to partner on the 754-unit project at 75 Morrissey Blvd. Pactolous and POB, which own the site, have sought to terminate their development agreement with Copper Mill, according to the suit.

The lawsuit, filed Thursday in Suffolk County Superior Court, was first reported by Banker & Tradesman. The complaint was signed by Sheehan Phinney attorneys Aaron Rosenberg, Steven Veenema and Stephanie Hoyer.

Copper Mill, POB and Pactolus didn't immediately respond to Bisnow's request seeking comment.

The dispute traces back to Dec. 18, 2024, when Boston-based Copper Mill reached a deal to buy the site from Chicago-based POB and Virginia-based Pactolus for $67.5M, according to the lawsuit. Because the buyer was seeking entitlements for a redevelopment, the parties agreed to schedule the deal's closing for 18 months later, in June 2026.

In March 2025, Copper Mill filed an application with the city detailing its plans to construct two buildings on the 2.2-acre site totaling 754 units, 150 of them set aside as income-restricted.

The Boston Planning & Development Agency Board approved the proposal in August 2025. But in the meantime, the seller was pushing to restructure its deal.

POB CEO Richard Holly had expressed surprise to Copper Mill CEO Andrew Flynn over the size of its plans for the site, according to the lawsuit. It said Holly remarked that if Copper Mill secures approval for such a project, its deal to sell the site for $67.5M would make the sellers "look like morons."

Holly then "consistently urged" Flynn to work together on the project as a joint venture, the lawsuit says.

Holly pitched Flynn on a broader venture that could pursue a series of projects in Boston. The lawsuit says he emphasized his relationships with investment giants including Starwood, Brookfield and KKR that could help finance the projects.

Flynn agreed to the partnership, and the parties formed a joint venture on Sept. 4, 2025, according to the lawsuit. It says Pactolus and POB jointly owned 64.35% of the JV, and Copper Mill owned 35.65%.

But after forming this partnership, the lawsuit says the defendants "worked to undermine the joint venture they had formed with Copper Mill, all while feigning efforts to benefit it."

The suit says the defendants failed to arrange the financing for the joint venture, claiming they refused to set up meetings between Copper Mill and prospective investors. It called the efforts to secure financing a "sham."

Meanwhile, it claims POB and Pactolus "were secretly marketing the party to third parties" and had approached the owner of an unnamed Boston real estate company with a new proposed deal that valued the property at $82.5M.

The defendants then sent Copper Mill a notice of termination of the joint venture agreement on June 30, the lawsuit says, adding that Copper Mill owes "significant outstanding balances" to third parties that had worked on its development plans.

Flynn sent a lengthy letter to the defendants on Aug. 13, providing notice of the claims it is now suing over and seeking a discussion, but the suit says the defendants "never substantively responded."

The suit rests on nine counts, including fraud, civil conspiracy and tortious interference with contract. It is seeking an unspecified amount of damages to be determined at trial.

If a development ultimately proceeds on the 75 Morrissey Blvd. site, it could benefit from the opportunity zone program, as Gov. Maura Healey included it in her proposed map for the tax incentive program's second iteration that goes into effect next year.

Copper Mill has had another issue with a development in Somerville's Davis Square this year. It proposed a 502-unit project in January, but in August, the developer said it was stepping away from the deal with the property owners, blaming the city for not supporting the project.