Fore River Urology in South Portland is leaving the Anthem insurance network starting on Aug. 1, according to a letter sent to its patients Monday.

The move affects about 10,000 patients who have an Anthem plan, according to Fore River. The independent health care provider said in its letter that Anthem has proposed reimbursement rates that would not cover the cost of providing care. The change will go into effect Aug. 1 for those with commercial plans, and Sept. 1 for Medicare Advantage.

“For more than four months, we have attempted to negotiate a contract renewal with Anthem, but unfortunately it has become clear that Anthem is not willing to reimburse Fore River Urology in a manner that would allow our practice to remain independent and be able to provide the high-quality, cost-efficient urological services that our patients deserve,” according to the letter.

“The reimbursement rates that Fore River Urology receives for services provided to Anthem’s members have been in place since our current contract with Anthem was agreed to in 2017. Since that time, our costs of providing services have skyrocketed as we have been forced, like most other healthcare providers, to continue to provide services to our patients in the midst of an unprecedented public health emergency. Despite these extraordinary circumstances, Anthem has proposed payment rates that would not even begin to cover the additional costs that we have been bearing over the past several years.”

Stephanie DuBois, Anthem spokeswoman, said in a statement that “Fore River Urology is demanding a nearly 50 percent increase in reimbursement rates, something Maine consumers cannot afford.

“We have offered substantial, yet reasonable increases each year over the next several years, which have so far been rejected by Fore River. It’s unfortunate they have chosen to announce their intention to leave our network, but we cannot agree to such unreasonable increases that would drive the high cost of healthcare in Maine even higher,” DuBois said. “Should Fore River follow through with its announcement to leave our network, we will work with our members to ensure they have access to the care they need from one of the many other urologists in our broad network.”

Fore River’s decision to leave the network would mean its patients with Anthem coverage would be forced to pay higher out-of-pocket costs.

Anthem is also locked in a much larger contract dispute with MaineHealth over billing conflicts with the health care network.

In early April, MaineHealth announced that Maine Medical Center in Portland was leaving the Anthem network starting in January because hospital officials say they are being shortchanged on numerous bills. The move would affect about 150,000 patients. Anthem officials counter that Maine Med is overcharging its patients for medications.

At 300,000 members, Anthem is the state’s largest insurer and represents 54 percent of the insurance market in Maine.