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.
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.