Tens of thousands of UnitedHealthcare members will now face higher out-of-pocket fees if they go to Wellstar Health System hospitals and doctors.

The contract between the two organizations ended Sunday without a new agreement. An estimated 80,000 United members will be affected.

Payment for medical services is the sticking point. United says the Wellstar demands for higher reimbursements are excessive, and the 11-hospital Wellstar says it’s seeking the same rates that other insurers are paying.

The nonprofit Wellstar dominates medical care in Cobb County and the suburbs northwest of Atlanta.

“Wellstar’s hospitals are already the most expensive in Atlanta, yet Wellstar refused to move off its demands for an egregious 37 percent price hike over three years that would have increased health care costs by more than $109 million,’’ the Minnesota-based company said in a statement Monday. “This is not sustainable or affordable for the people and employers we serve.’’

Last week, Wellstar stated that it had “been underpaid by United for years.’’

Josh Berlin, of Atlanta-based consulting firm rule of three LLC, said that the termination of the contract isn’t surprising.

Wellstar, he said, had a previous dispute with Anthem a couple of years ago. United had a messy contract rift with Northside Hospital that was resolved in August, but only after Northside’s Gwinnett facilities went out of network for months.

In past years, a large majority of contract negotiations between hospital systems and insurers would be resolved before a contract was severed. But more recent battles have gone past the deadlines for reaching a new deal.

“Unfortunately, this continues a trend that has emerged for some time now in a variety of markets around the country,” Berlin said. “The most unfortunate aspect of all of this is the patient or consumer suffers the most, despite short-term remedies offered by a provider.’’

Retirees under the ​​State Health Benefit Plan’s UnitedHealth Medicare Advantage plan will still have in-network access, Wellstar and UHC said Monday.

Negotiations on the overall contract are continuing, Wellstar said late Monday. “We remain hopeful that we can come to a new agreement quickly that prioritizes patient care,” the Marietta-based organization said.