The airlines said they filed a notice of appeal with the 1st U.S. Circuit Court of Appeals, following the terms of their agreement.

The Justice Department, which sued to block JetBlue’s proposed $3.8 billion purchase of Spirit, declined to comment.

JetBlue and Spirit are the nation’s sixth- and seventh-largest carriers. JetBlue, which outbid Frontier Airlines, said it needed to acquire Spirit to compete more effectively against even bigger airlines.

But on Tuesday, a federal judge in Boston ruled that the deal violated antitrust law. The U.S. Justice Department had sued to stop the deal, arguing that consumers would be harmed and forced to pay higher fares if Spirit — the nation’s biggest discount airline — were eliminated.

The airlines announced their appeal in a statement that provided no other details.

Earlier Friday, Spirit said that a strong holiday-travel season in December boosted its fourth-quarter revenue. The Miramar, Florida-based airline also said that it is trying to refinance $1.1 billion in debt that is due for payment in September 2025.

Spirit also said that negotiations with Pratt & Whitney over engines that need to be reworked — resulting in the grounding of an average of 26 planes a day throughout 2024 — “have progressed considerably since October.” The airline said it expects compensation that will provide “a significant source of liquidity over the next couple of years.”

Spirit has been losing money since the start of 2020. Some analysts said it could face bankruptcy without the merger with JetBlue.

The airlines announced their intention to appeal U.S. District Judge William Young’s ruling after the stock market closed on Friday.

Shares of Spirit, which fell 62% over three days following the ruling, gained 17% in regular trading Friday, and rose another 13% in after-hours trading. JetBlue’s shares fell 2% in extended trading.