CONCORD, N.H. – The New Hampshire Medical Society has joined a class action lawsuit that charges nine of the nation’s largest medical insurers with conspiring against doctors.

The suit accuses the insurers of forcing doctors into unfair contracts with reduced payments, withholding payments for medical procedures and failing to provide fee schedules when contracts are negotiated.

New Hampshire joins state medical associations from Maine and 17 other states in the federal suit, which is filed in Miami.

“It’s been a take-it-or-leave attitude from the insurers for too long,” said Palmer Jones, executive vice president of the New Hampshire Medical Society. “Physicians have difficulty working under these health plans.

“We hope this sends a strong message that physicians are concerned about their ability to provide good patient care.”

The two largest insurers in the state, Cigna HealthCare and Anthem Blue Cross and Blue Shield, are named in the suit with seven other large managed care companies, including Aetna, United HealthCare and Humana.

Spokesmen for Anthem and Cigna declined to comment.

The suit is unusual as it claims insurers violated the federal Racketeer Influenced and Corrupt Organization Act, or RICO, to conspire against the medical industry.

The RICO act was designed to break the influence of organized crime. The suit does not allege any connection between insurers and organized crime, but accuses insurers of colluding to keep payments artificially low.

Lawyers said it was the first time the RICO act had been invoked to prosecute the health care industry.

Other state medical associations in the lawsuit are in Alaska, Arizona, California, Colorado, Connecticut, Florida, Georgia, Hawaii, Louisiana, Maine, Nebraska, New Jersey, New York, North Carolina, South Carolina, Tennessee, Texas and Washington.

The societies represent more than 600,000 doctors.

Parties to the lawsuit said they were motivated less by money and more by a desire to compel insurers to change their negotiating tactics.