Frontier Airlines announced Monday that its customers will no longer be able to book tickets on Expedia, a popular third-party ticketing website.

The move is the latest attempt by the Denver-based carrier to steer customers toward booking directly on the airline's website, FlyFrontier.com.

"The contract with Expedia was up for renewal, but an agreement could not be reached," said Kate O'Malley, spokeswoman for Frontier in an e-mail.

Unlike its low-cost carrier competitor at Denver International Airport — Southwest Airlines — Frontier tickets will still be available for now on other third party travel sites, such as Travelocity, Orbitz and Priceline.

In September, Frontier began penalizing passengers who booked on third-party sites by charging more in fees, awarding them half the frequent flier miles, and not allowing them to get a seat assignment until check-in.

Frontier is offering a fare sale on its website between Feb. 25 and March 3 to encourage customers to book directly with the airline. Air travel must be completed by May 22.

Kristen Leigh Painter: 303-954-1638, kpainter@denverpost.com or twitter.com/kristenpainter