In a potentially costly setback, a judge for the federal Department of Transportation found Tuesday that higher terminal fees the city airport agency imposed on low-cost and international carriers at Los Angeles International Airport earlier this year are unreasonable and discriminatory.

The ruling, if upheld, could cost Los Angeles World Airports millions of dollars and throw into question how the agency would pay for added security since 9/11 and improvements at timeworn LAX.

The fee increase, imposed by the city Airport Commission, nearly quadrupled rent and maintenance costs for domestic carriers in Terminals 1 and 3. Airport officials argued that the jump was necessary because they were subsidizing the airlines. Carriers contended that the higher costs put them at a competitive disadvantage, because airlines with long-term leases would continue to pay lower terminal rent.

The carriers appealed the fee increase to the U.S. Transportation Department.

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