A federal judge on Wednesday ruled against Anthem Inc. in its quest to buy rival health insurer Cigna Corp., saying the merger could potentially lead to an increase in costs and less competition.

U.S. District Judge Amy Berman Jackson issued the ruling against Anthem.

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Jackson said the merger would significantly reduce competition in the insurance market, particularly for large employers. Just four insurers sell to companies with at least 5,000 employees spread across multiple states, and the judge says Cigna and Anthem aggressively compete for their business.

Reuters reported the Anthem, Cigna merger was a projected $54 billion deal.

A spokeswoman for Anthem has said officials for the company are reviewing the decision.

According to Reuters, the U.S. Department of Justice sued in July to block the Anthem-Cigna deal and another major acquisition, Aetna's $33 billion plan to buy Humana. A judge rejected the Aetna-Humana union last month.

The Associated Press contributed to this report.