The cities of Edmonds and Mukilteo and other opponents of commercial air service at Paine Field have filed a notice to challenge the decision in federal court.
The Daily Herald reports the notice filed with the federal court of appeals could lead to a hearing in April.
The Federal Aviation Administration determined in December that flights proposed by Allegiant Air and Horizon Air at the Snohomish County airport would not significantly increase noise, traffic or air pollution in nearby communities.
The county is starting to plan for a terminal. Although most county officials oppose commercial flights at Paine Field, the county is required to provide space to airlines if it wants to continue receiving federal money for airport maintenance and projects.