American Airlines (AA, Dallas/Fort Worth) and JetBlue Airways (B6, New York JFK) will start to wind down their Northeast Alliance later this week, the two carriers announced, after a federal court ordered in May that they end the agreement.

The airlines have coordinated their schedules through the alliance, have exchanged airport slots and gates, and implemented frequent flyer reciprocity. However, the Department of Justice (DOJ) filed a lawsuit against the venture, arguing that it harmed competition, and eventually a judge agreed to give the airlines 30 days to end it.

American and JetBlue tried to salvage parts of the deal, but in early July JetBlue said it had decided not to appeal the ruling and had instead begun a gradual winding down of the three-year-old partnership, a process it said could take several months.

Now, both airlines say that they have “begun to work through the initial steps to wind down the pro-competitive, pro-consumer Northeast Alliance” and that “codeshare flights between American and JetBlue will no longer be available for sale starting July 21.” Customers will have until the end of the day on July 20 to update any existing bookings that carry each other’s member numbers.

“This is just the first step in the wind-down process that will take place over the coming months. We will continue to work with the JetBlue team to ensure customers who have existing codeshare bookings can travel seamlessly without disruption to their travel plans,” American Airlines assured.

Dave Fintzen, vice president of the Northeast Alliance at JetBlue, said that “we believe the US Department of Justice’s position [opposing the aspects of the alliance] misses the mark. With the court’s recent ruling and the termination of the NEA, we have to sunset them in short order.”

American Airlines has said it still plans to challenge the court ruling. The alliance was part of its strategy to increase revenue by relying more heavily on partners to ferry passengers to and from uncompetitive markets. It had also helped the carrier to compete more forcefully in the New York market, where it had previously been losing money. JetBlue, meanwhile, is now likely to focus on its proposed merger with Spirit Airlines (NK, Fort Lauderdale International), which had compounded the DOJ’s competition concerns.