Harvard Pilgrim Health Care will be discontinuing its Medicare Advantage program, known as First Seniority Freedom, at the end of the year, leaving 22,000 seniors in Massachusetts, Maine and New Hampshire to seek coverage elsewhere.

The company’s decision comes after Medicare officials created a new requirement that insurers form a network of doctors who agree to participate in the program for negotiated reimbursement amounts. Current rules allow patients to seek care from any doctor.

“We became concerned by the long-term viability of Medicare Advantage programs in general,” says Harvard Pilgrim vice president Lynn Bowman. “We know that cuts in Medicare are being used to fund national health care reform. And we also had concerns about our ability to build a network of health care providers that would meet the needs of our seniors.”

Harvard Pilgrim is urging customers to switch to a new Medicare Supplement plan available beginning in October. Unlike First Seniority Freedom, the new Medicare Supplement plan will be regulated by the Massachusetts Division of Insurance.