(CNN Money) — The Justice Department on Thursday filed notice that it is appealing a judge’s approval of AT&T’s purchase of Time Warner.

Judge Richard Leon, who presided over the lawsuit the DOJ had brought to block the deal, ruled last month that the government had failed to show that the deal violates antitrust law, and in his opinion ripped apart its case. AT&T has since closed the acquisition of Time Warner, including CNN.

AT&T has since re-named the division WarnerMedia, created as a separate unit from the rest of the company, in part in case of an appeal.

The Justice Department sued to stop the deal last year, saying that a distributor, AT&T, owning the likes of HBO, CNN and Warner Bros. would harm consumers by causing an increase in prices and would hurt innovation and competition. But after a six week trial, Leon said he didn’t buy that, and signed off on the deal with no conditions and knocked down the government’s contentions point by point.

“The Government has failed to meet its burden of proof to show that the merger is likely to result in a substantial lessening of competition,” he wrote in his ruling.

Using unusually strong language, Leon discouraged the Justice Department from asking him to put the ruling on hold while it considers an appeal. He said such a stay would be “manifestly unjust” because it would have the effect of killing the acquisition. The Justice Department did not seek a stay, and the deal closed.

Now the case will go to the D.C. Circuit Court of Appeals, where a three-judge panel will hear the appeal.

In theory, the case could end up in front of the Supreme Court, something some people in the legal community have been hoping for, since the Supreme Court has not taken up a merger case since the 1970s.

“The Court’s decision could hardly have been more thorough, fact-based, and well-reasoned. While the losing party in litigation always has the right to appeal if it wishes, we are surprised that the DOJ has chosen to do so under these circumstances. We are ready to defend the Court’s decision at the D.C. Circuit Court of Appeals,” AT&T General Counsel David McAtee said in a statement.

Spokespeople for the Justice Department declined to comment.

The-CNN-Wire™ & © 2018 Cable News Network, Inc., a Time Warner Company. All rights reserved. (Photo: AP)