The American Medical Association, the largest association of doctors in the US, wants federal antitrust enforcers to smack down two proposed mergers between big health insurance companies: the combining of Aetna and Humana, and of Anthem and Cigna. The two mergers, if approved, would shrink the number of major national health insurers from five to three.

In a 17-page letter sent to the Department of Justice Antitrust Division on Wednesday, AMA CEO James Madara wrote that the association studied the planned mergers and concluded that they would likely hamper access, affordability, and quality of patient care, plus make it harder for physicians to negotiate competitive insurer contract terms.

“A growing body of peer-reviewed literature suggests that greater health insurer consolidation leads to price increases, as opposed to greater efficiency or lower health care costs,” Madara wrote.

The mergers would ease pressure on insurers to provide wide networks. Small or restrictive networks drive patients to seek care from more expensive, out-of-network providers, Madara noted. The planned deals may also lead to physicians getting reimbursed at low, non-competitive rates. This could lead to physicians being “forced to spend less time with patients to meet practice expenses,” and practices cutting back on technology, training, and staff that are crucial to quality care.

In an e-mail to the Huffington Post, Aetna spokeswoman Cynthia Michener wrote: "We believe the combination of Aetna and Humana will improve the health care system and offer consumers more choices and greater access to higher quality, more affordable care."

Similarly, Anthem spokeswoman Jill Becher wrote in an e-mail: "We will deliver for consumers by operating more efficiently to reduce our own costs, while enhancing our ability to manage the cost drivers that negatively impact affordability for consumers."

The merger plans will be reviewed by the Department of Justice, the Federal Trade Commission and state regulators. The American Hospital Association has also opposed the deals.