Frontier Airlines will begin new service between its Denver hub and Calgary International Airport in Alberta, Canada beginning May 25. The two daily non-stops between Denver and Calgary will utilize Frontier’s JetExpress service operated by Horizon Air. The new service will be the first U.S. low-cost carrier flights into Canada and Frontier’s second international destination, after Mexico. Members of EarlyReturns will earn double miles for travel to and from Calgary through June 30.