A federal appeals court has upheld a preliminary injunction barring Delta Air Lines Inc., the world's biggest airline operator, from terminating a regional flying contract with Mesa Air Group Inc. subsidiary Freedom Airlines.

Phoenix-based Mesa had said that the termination of the contract, if successful, would cripple its airline.

Mesa said last year that the contract amounted to $20 million in monthly revenue for the parent company, or about 20 percent of its total sales for 2007.

Mesa won a preliminary court injunction from the federal district court in Atlanta to block the contract termination, and the 11th U.S. Circuit Court of Appeals, also in Atlanta, affirmed that decision Wednesday.

Delta says it will continue to fight to preserve its right to terminate the contract.