Competition is intense for new daily service to Ronald Reagan Washington National Airport, and two of Colorado's largest airlines are joining in the fray.

Frontier and Southwest airlines are urging friends, family and fliers to write the U.S. Department of Transportation in support of their bids for four slot pairs to the Washington, D.C., airport.

The slots are available under the Federal Aviation Administration re-authorization bill signed Feb. 14 by President Barack Obama. The legislation allows new flights to cities beyond Washington National's traditional 1,250-mile service perimeter.

Seven airlines have applied: Frontier, Southwest, Air Canada, Alaska, JetBlue, Sun Country and Virgin America.

Southwest Airlines plane.
Southwest Airlines plane. (AP)

Southwest's application would not include a Colorado city. The Dallas-based carrier is seeking the slots to fly nonstop between Washington National and Austin-Bergstrom International Airport in Texas. The flight would continue to San Diego, with a return flight.

Frontier's proposal is for first-ever service between Washington National and Colorado Springs. It also would continue to San Diego, with a return trip on the same route.

Frontier has gained the support of the Colorado Springs business community.

A group of Colorado Springs interests has launched a community letter-writing campaign to back Frontier's application. Support also can be submitted on frontierairlines.com.

The DOT is expected to make a decision in May. Officials at Frontier and Southwest said they could begin service this summer.

Ann Schrader: 303-954-1967, aschrader@denverpost.com