The Department of Justice will review a $54 billion deal between health insurer Cigna and drug middleman Express Scripts.
The review, first reported by Bloomberg, comes amid concerns about increasing consolidation in healthcare.
The Justice Department has moved to stop healthcare deals before because of antitrust concerns, most notably suing to block a deal between insurers Cigna and Anthem and another between Humana and Aetna.
Both deals fell apart after DOJ opposition.
DOJ and the Federal Trade Commission have not said if they will review the proposed deal between Aetna and drugstore chain giant CVS, which has moved to create its own pharmacy benefit manager business.
A pharmacy benefit manager oversees a drug plan for employer or group health plans.
The groups usually negotiate with drugmakers for rebates to reduce prices, but they have been criticized for not sharing enough of the rebates with consumers.
