American Airlines has escalated its legal fight with a leading ticket-reservations system by accusing Sabre Holdings Corp. of organizing a boycott of American by travel agents.

The airline said in a court filing that Sabre is punishing American for its effort to distribute more tickets directly to travel agents.

Sabre denied the charges and said American is using the courts to extract a better distribution contract from Sabre.

Sabre, which was once part of American but is now owned by private buyout firms, provides information about flights and fares to travel agencies. American wants to reduce ticket-distribution costs by providing the information directly to travel agents, cutting out middlemen like Sabre in many cases.

American, a unit of AMR Corp., is suing Texas-based Sabre and another flight-information provider, Travelport Ltd., in a state court in Fort Worth and lodged the boycott accusation in a filing Wednesday.

Last month, Sabre agreed to keep listing American flights on its service until the legal dispute is settled.