The American Medical Association, which represents US physicians, urged the Justice Department on Wednesday to stop CVS Health’s plan to buy insurance provider Aetna, saying the deal could result in higher prices for prescription medicines.

The AMA said the $69 billion deal, announced in December, would lead to a “substantial reduction” of competition in pharmacy benefit (PBM) services market and the Medicare Part D prescription drug plan for seniors.

The AMA said the deal would increase concentration in 10 of the 34 Medicare Part D regional markets to the point where it is presumed likely to increase market power.

“CVS and Aetna … operate as rivals in some of the same markets, raising substantial concerns,” said AMA president Barbara McAneny in a statement.

McAneny said the merger would mean higher prices, less choice and stifled innovation in PBM services, health insurance and pharmacy services.

CVS said in a statement that it strongly disagreed with the AMA’s assessment of the deal.

“We believe that competition within each of the business segments in which we operate — pharmacy benefit management, pharmacies and insurers — is fierce and will remain so,” the company said in a statement.