Physician groups are warning that seniors could face challenges getting medical care because UnitedHealthcare is cutting doctors from its Medicare Advantage network.

The Connecticut State Medical Society said Thursday that UnitedHealthcare had sent thousands of letters to doctors in the state saying they had been “terminated without cause” from the insurer’s Medicare Advantage network, effective Feb. 1.

“Many patients have been with their doctors for decades,” the medical society said in a statement. “United’s decision will disrupt these long-term patient relationships. For those patients with chronic health issues, the resulting lack of care continuity could result in poor health outcomes. United’s decision may also make it more difficult for seniors to access needed medical care. For the average patient, driving an extra five miles for care can be an inconvenience. For seniors with limited mobility, those same five miles can be a significant barrier to access.”

UnitedHealthcare has approximately 58,000 Medicare Advantage members in Connecticut.

UnitedHealthcare has not released many details about its network changes. In a statement Wednesday, spokesman Ben Goldstein said the company is “building a network of health care providers that we can collaborate with more closely to have the most positive impact on the quality of care for our members. This will encourage better health outcomes and ultimately lower costs.”

Goldstein said affected members were being notified. The changes don’t affect people covered by UnitedHealthcare Medicare supplement plans, he said.

He did not answer questions about how many doctors were being terminated from the Medicare Advantage network or whether the company is considering making similar changes to its networks for other types of plans.

The Fairfield County Medical Association reported earlier in the week that 2,250 doctors statewide were being terminated from UnitedHealthcare’s Medicare Advantage network, representing approximately 19 percent of the current network. The group also warned that company officials “would not rule out the possibility that the company may, at some point in the future, also reduce the size of its physicians’ panel for other commercial products.”

The network flap comes days before the Medicare open enrollment period begins. Between Oct. 15 and Dec. 7, seniors can sign up for Medicare Advantage plans, drop the program in favor of “original” Medicare, and select Medicare Part D prescription drug plans.

Dr. Michael F. Saffir, the medical society’s president, said the timing of the changes was “questionable.” “How can seniors make informed decisions when their own doctors don’t even know whether they’re in the United network?” he said.

There was also confusion about the notices. Many doctors got more than one letter, and the medical society said UnitedHealthcare officials had said that some doctors who got the notice could still be in the Medicare Advantage network. Company officials couldn’t confirm whether all affected doctors had received the notice, the medical society added.

The medical society said the American Medical Association is investigating “similar situations in other states.”

In response to the medical society’s comments, Goldstein said, “We offer our members one of the most extensive networks of health care providers in Connecticut and remain committed to ensuring they have continued access to quality, affordable care. Members with questions are encouraged to call the customer service number on the back of their member ID card for more information.”

Saffir questioned the wisdom of making such a broad cut to the provider network.

“Even if you need to cut something, you use a scalpel, not a chainsaw,” he said. “The approach is so disruptive and abrupt that you’re going to alienate both doctors and patients.”

Saffier said he was concerned that other insurers could also decide to reduce their physician networks as a way to cut costs in the Medicare Advantage program. But he said negative reaction from doctors and patients could give them pause before taking such a broad approach.