The Justice Department will appeal the AT&T-Time Warner merger approval, according to a court document filed Thursday.
Shares of AT&T slipped 1 percent in after-hours trading Thursday, CNBC reported.
In June, a federal judge ruled that the $85.4 billion deal was legal and imposed no conditions on the merger.
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At the time, the Justice Department expressed its disappointment with the ruling. The government argued that the deal would make the pay-TV market "less competitive and less innovative."
AT&T, the No. 2 wireless carrier in the U.S., maintains that the deal would help the company attract customers — and compete with companies like Amazon and Netflix — by bundling entertainment with mobile service.