MIAMI — American Airlines Group announced it will no longer sell tickets via the popular online ticket agent, Orbitz.

The change is effective immediately for all American Airlines fares. US Airways fares will disappear from the site effective September 1st. The decision delists the world’s largest airline from the site, along with several subsidiary sites including and ebookers. The news sent shares of Orbitz tumbling down as much as 5% in trading.

“We have worked tirelessly with Orbitz to reach a deal with the economics that allow us to keep costs low and compete with low-cost carriers,” said Scott Kirby, President of American in a short statement. The carrier has not dropped similar online ticket sites such as Kayak or Expedia, suggesting that the problems stem from a poor financial relationship rather than a problem with online ticket retailers.

Tickets already purchased via the site will be unaffected, though changes to such itineraries must go through the carrier. It will not affect corporate contracts handled through Orbitz for Business.

It is not the first falling out that American has faced with Orbitz. The carrier pulled its fares from the website in late 2010 and into 2011 after a contract dispute took an ugly turn. The matter, which surrounded how transactions were funneled through distributors such as Orbitz into American’s system, wound up in federal court when the airline slapped the site with an antitrust lawsuit (the suit also involved Sabre and Travelport). The suit claimed that Orbitz intentionally raised prices and blocked competition. A federal judge wound up ordering American to post its fares on the site in June of 2011.The dispute was settled in April of 2013, nearly two years later.

Orbitz first appeared online in 2001. It was created as a joint venture between five major airlines, American included, in order to compete against newly created online travel agencies such as Expedia and Travelocity.