United Airlines is threatening to pull fares from several Expedia Group sites amid a contract dispute, the online travel agency said in a lawsuit.

In the suit, filed Monday in federal court in New York, Expedia alleged United was using its weight as one of the biggest U.S. airlines to renegotiate its agreement.

United said that Expedia has "refused to engage in constructive discussions" and that it informed Expedia that it "expects" to pull fares for travel Oct. 1, 2019 or later. United's contract with Expedia expires in the fall.

Expedia asked the court to stop United from blocking fares and seat availability beyond Sept. 30, 2019.

United said if it pulls fares for flights beyond Sept. 30, Expedia wouldn't be able to book or change tickets. That would apply to Expedia's namesake travel booking site as well as other brands like Orbitz and Travelocity beyond that date. United flights on Expedia's corporate-travel platform Egencia would not be affected.

"Out of concern for the growing number of customers at risk, we sent Expedia a letter last week, months in advance of the expiration date, formally notifying Expedia that United intends to prohibit Expedia from booking tickets for travel October 1 and beyond," United said in a statement. United said that measure is to avoid having passengers unable to make changes to their tickets through Expedia when the contract expires.

At the time the lawsuit was filed, United had provided flights to Expedia through Jan. 6, 2020, and customers had reserved more than 2,000 seats, the suit said.

United said more than 70 million tickets for its flights were purchased through online travel agencies and fare-search sites last year.

Airlines and online travel agencies have often had a contentious relationship as airlines try to drive more traffic to their own sites to save on the cost of distributing tickets. JetBlue Airways in 2017 announced it would pull its fares from a dozen online travel agencies. Southwest Airlines doesn't post its tickets on online travel agency sites.