The company is the largest Medicare Advantage insurer in the country, with nearly 3 million members. More than 14 million older or disabled Americans are enrolled in Medicare Advantage plans, an alternative to traditional Medicare that offers medical and usually drug coverage but members have to use the plan’s network of providers. …

UnitedHealthcare has begun telling members about the network changes. But there is now less than two weeks before the Dec. 7 deadline for choosing new coverage next year. Timing is crucial since once they sign up, most Advantage beneficiaries are locked into their plans for the year. Losing a doctor does not constitute an exception to the rule. Insurers can drop providers any time with 30 days advance notice to members.

Several medical associations are encouraging doctors to appeal the cancelations, which could make it more difficult for seniors to choose a plan in the time remaining. Neither Medicare, which oversees the Advantage plans, nor UnitedHealthcare would disclose how many providers will be dropped.