Details of the ruling that stopped the merger of H&R Block and TaxAct surfaced Thursday when U.S. District Judge Beryl Howell released her legal reasoning.

In the 86-page ruling, Howell discussed several key arguments in her decision to reject the merger. She agreed with the Department of Justice’s (DOJ) belief that the deal would harm competition in the market for digital tax-preparation services, which only has three significant players: H&R Block, TaxAct and Intuit, the maker of TurboTax.

Responding to the ruling, DOJ antitrust chief Sharis Pozen said she was “pleased that the court agreed with the department’s main arguments of the case.”

However, Howell disagreed with the Justice Department over its labeling of TaxAct as a “maverick” firm; instead, she accepted the department’s basic argument and wrote, “The Court finds that TaxACT’s competition does play a special role in this market that constrains prices.”

DOJ merger challenges are rarely taken to trial, making this ruling the first since 2004. Still, Howell’s ruling may be of interest for the upcoming AT&T case involving its purchase of T-Mobile, because the deal also involves the possibility of eliminating competition within a national market.

But AT&T General Counsel Wayne Watts thinks otherwise, saying the H&R Block case “has nothing in common with ours.”