The U.S. Justice Department said on Thursday it would appeal a federal judge¡¯s approval of AT&T Inc¡¯s $85.4 billion acquisition of Time Warner, raising the prospect that the deal could be undone.

The Justice Department opted in June not to seek an immediate stay of the court¡¯s approval of the merger, allowing the merger to close on June 14, though the Justice Department still had 60 days to appeal the decision approving the merger. The government¡¯s court filing did not disclose on what grounds it intends to challenge the approval.

AT&T and the Justice Department did not immediately comment.

AT&T shares fell 1 percent after the bell.

The merger, first announced in October 2016, was opposed by President Donald Trump. AT&T was sued by the Justice Department, but won approval from a judge to move forward with the deal in June following a six-week trial.

Judge Richard Leon of U.S. District Court for the District of Columbia ruled that the tie-up between AT&T¡¯s wireless and satellite businesses with Time Warner¡¯s movies and television shows was legal under antitrust law. The Justice Department had argued the deal would harm consumers.