Six Connecticut residents have filed a proposed class-action lawsuit against Hartford HealthCare, accusing the not-for-profit health system of anticompetitive business practices that have driven up prices.

The complaint, filed Monday in Hartford District Superior Court, says Hartford’s prices are “routinely” more than 20% higher than its nearest competitor, and the prices for high-volume procedures like colonoscopies and blood transfusions are often hundreds of dollars more than nearby hospitals .

“Through its aggressive contracting practices, acquisition strategy and pricing, Hartford HealthCare is overcharging consumers and harming the residents, small businesses and taxpayers of Connecticut,” E. Danya Perry, a partner at the plaintiff’s law firm Perry Guha, said in a statement. “Our suit seeks to put an end to Hartford HealthCare’s anticompetitive behavior, which has been driving up insurance premiums across the state.”

The lawsuit seeks to halt the alleged unfair practices and reimburse Connecticut residents for amounts they’ve overpaid for health insurance as a result. It says residents overpay tens of millions of dollars every month in premiums, deductibles coinsurance and copays.

A spokesperson for Hartford HealthCare did not return a request for comment.

The case is very similar to the one filed last month by Saint Francis Hospital, which is located just a few miles away from Hartford HealthCare’s flagship Hartford Hospital. Saint Francis is also accusing Hartford HealthCare of anticompetitive behavior that’s resulted in higher prices and lower quality for patients. Saint Francis also said Hartford bullies physicians into anticompetitive contract terms and seeks to force the system to divest the physician practices it bought since 2020.

The residents’ lawsuit claims Hartford HealthCare has acquired numerous facilities over the years and is now using its market power to limit competition and hike prices. The complaint claims inpatient stays at Hartford Hospital cost about $4,000 more than at a hospital two miles away.

In particular, the lawsuit accuses the health system of buying “must have” hospitals, those that are the only inpatient providers in their respective communities and therefore must be included in insurance networks. The suit says Hartford then uses an “all-or-nothing” ” negotiating tactic with insurers, where it requires them to include all of its hospitals in their network—including the expensive ones in competitive areas like Hartford—even if they only need access to a “must have” hospital.

Sutter Health, a not-for-profit system based in Sacramento, California, recently paid $575 million to settle similar allegations, including that it uses all-or-nothing contracts. It’s also currently on trial in San Francisco in an almost identical case brought by businesses that paid for their employees’ health insurance.

Much like the Sutter case, the residents’ case against Hartford HealthCare also says the Connecticut system used its dominant market power to prevent insurers from rolling out cheaper health plans for residents.

“Hospital consolidation is a leading cause of rising health care costs nationwide,” Jamie Crooks, managing partner of Fairmark Partners, another law firm representing the residents, said in a statement. “These allegations show how a dominant system such as Hartford HealthCare chooses to abuse its market power to charge far higher prices than would otherwise be possible in a competitive market. Antitrust laws exist to protect consumers in these exact situations.”