Iowa’s senator has raised concerns about proposed mergers involving Connecticut insurers, the Hartford Business Journal reports.

In a letter to Makan Delrahim, the assistant attorney general leading the Justice Department’s antitrust unit, Senate Judiciary Committee Chairman Chuck Grassley said Bloomfield-based Cigna’s proposed $67 billion acquisition of pharmacy benefits manager Express Scripts and CVS Health’s $69 billion purchase of Hartford-based Aetna would negatively affect market competition.

Citing a new Kaiser Family Foundation report, Grassley said the combined companies, in addition to UnitedHealth and Humana, would control 86 percent of standalone drug plan enrollees and 71 percent of all Medicare Part D enrollees.

“Part of Congress’ role is to encourage new strategies and experimentation among these market participants to drive down drug prices,” Grassley wrote. “To that end, vertical integration, like the proposed transactions, can often result in increased efficiencies and consumer benefits, and should be evaluated accordingly.”