By David ShepardsonWASHINGTON (Reuters) -The chief executives of low-cost carriers Allegiant Airlines and Frontier Airlines will testify before a U.S. Senate Judiciary antitrust subcommittee on Tuesday on air carrier competition, congressional aides said. Allegiant Airlines CEO Greg Anderson and Frontier Airlines CEO Barry Biffle are among the witnesses that will testify, as will Sharon Pinkerton, a senior vice president at Airlines for America, which represents United Airlines, Delta Air Lines, American Airlines, Southwest Airlines and others. AIR TRAFFIC CONTROL AND LOW-COST AIRLINES IN FOCUSAirlines for America said it looks forward "to highlighting how robust competition has led to historically low fares, a wide availability of options and quality customer service which has resulted in record high demand." The group added "the largest threat to having a healthy, competitive airline industry is our nation’s antiquated, understaffed air traffic control system." "Maybe that's why United executives can't stop yapping about us," the airline said.