LOUISVILLE, Ky. (WDRB) -- The U.S. Department of Justice filed a lawsuit Thursday to block the $37 billion takeover of Louisville-based Humana by Aetna.

Federal officials also filed suit to block the $54 billion Anthem-Cigna merger, which together would reduce the five largest health insurers in the country to three.

The Justice Department said in its lawsuit that Aetna's swallowing Humana would create an unacceptable reduction in choices for seniors who buy Medicare Advantage plans, which are privately run versions of the government's healthcare program for those over 65.

"If allowed to proceed, this merger would enhance Aetna’s power to profit at the expense of seniors who rely on Medicare Advantage and individuals and families who rely on the public exchanges for affordable health insurance," the department said in its complaint against Humana and Aetna.

In a statement, Aetna and Humana said they will "vigorously defend" the merger.

"A combined company will result in a broader choice of products, access to higher quality and more affordable care, and a better overall experience for consumers," the companies said. "Aetna and Humana look forward to making this clear in court, where a judge will review the transaction based on its merits."

The merger threatens to eliminate Louisville's largest corporate headquarters, though officials have said that the city would become the epicenter for Aetna's government business, such as Medicare Advantage, and gain more jobs than it loses.

Humana employs more than 12,000 people in Louisville, the vast majority of which work downtown.

Analysts have speculated that the Humana-Aetna deal could be saved if the companies agree to sell off certain parts of their businesses before closing the merger.

But William Baer, a top Justice Department official, said in a news conference Thursday that the so-called divestitures offered by the health insurers have been "incomplete and impractical."

"There are some mergers that can be saved through divestitures," Baer said. "We have nothing to suggest these can."

Here is the complaint:

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