Overall, Sutter said, “healthy competition and choice exists across Northern California” for consumers seeking medical care, and that its charges for an inpatient stay are lower than what other nearby hospitals charge.

“Sutter Health is proud to save patients, government payers and health plans hundreds of millions of dollars each year by providing more efficient and integrated care,” the statement said.

This high-profile legal fight will attract attention from employers and policymakers across the country amid growing alarm about the financial implications of industry consolidation. Large health systems are gaining market clout and the ability to raise prices by acquiring more hospitals, outpatient surgery centers and physicians’ offices.

Martin Gaynor, a health care economist at Carnegie Mellon University, said California’s lawsuit may portend more litigation at the state level.

“There are a number of markets in the U.S. that are dominated by one very large, powerful health system,” Gaynor said. “It could be that we’re going to see a new level of activity by state antitrust enforcers looking at competition in their own backyards.”

The complaints about Sutter’s high prices and market power have persisted for years.

A 2016 study found that hospital prices at Sutter and Dignity Health, the two biggest hospital chains in California, were 25 percent higher than at other hospitals around the state. Researchers at the University of Southern California said the giant health systems used their market power to drive up prices — making the average patient admission at both chains nearly $4,000 more expensive.

This week, researchers at University of California-Berkeley issued a report that examined the consolidation of the hospital, physician and health insurance markets in California from 2010 to 2016. The authors said 44 of California’s 58 counties had “highly concentrated” hospital markets.

The problem is worse in Northern California and the report said prices for medical procedures are often up to 30 percent higher there than in Southern California, which has more competition.

“Consumers are paying more for health care as a result of market consolidation. It is now time for regulators and legislators to take action,” according to the report by the Petris Center on Health Care Markets and Consumer Welfare at UC-Berkeley.

After the report was issued Monday, Becerra said his office would be reviewing those findings and pledged to apply more scrutiny to health care mergers and anti-competitive practices across the state.

Sutter Health has gobbled up doctor practices across the Bay Area, gaining market muscle that has pushed costs upward. Obstetricians employed by Sutter Health, for example, are reimbursed about three times more for the same service than independent doctors, according to a KHN review of OB-GYN charges on several insurers’ online cost estimators. It’s a key reason why Northern California is the most expensive place in the country to have a baby.

Becerra’s lawsuit could build off a similar civil case filed in 2014 by a grocery workers’ health plan.

The plaintiffs in that case, scheduled for trial next year, allege Sutter is violating antitrust and fair competition laws. The plaintiffs have been requesting documents related to contracting practices, such as “gag clauses” that prevent patients from seeking negotiated rates and choosing a cheaper provider. They also are challenging “all-or-nothing” terms that require every facility in a health system to be included in insurance networks.

In November, the state judge handling the grocery workers’ case said Sutter was “grossly reckless” when it intentionally destroyed 192 boxes of documents that employers and labor unions were seeking in the lawsuit. San Francisco County Superior Court Judge Curtis E.A. Karnow said Sutter destroyed documents “knowing that the evidence was relevant to antitrust issues. … There is no good explanation for the specific and unusual destruction here.”

The lead plaintiffs, the United Food and Commercial Workers and its Employers Benefit Trust, are a joint employer-union health plan that represents more than 60,000 employees, dependents and retirees. The court certified its case as a class action in August, allowing hundreds of other employers and self-funded health plans to potentially benefit from the litigation.

In addition to its 24 hospitals, Sutter’s nonprofit health system has 35 surgery centers, 32 urgent-care clinics and more than 5,000 physicians in its network.

California Healthline reporter Ana Ibarra and KHN senior correspondent Jenny Gold contributed reporting.