Wichita ? The Federal Aviation Administration has given city officials 30 days to come up with a plan to address differences in economic subsidies for AirTran Airways and Delta Air Lines.

The FAA said in an April 6 letter to the city that its subsidies to AirTran constituted “unjust economic discrimination” against Delta. Both airlines provide daily service from Wichita to Atlanta.

Delta, which plans to address the City Council on Tuesday, wants equal access to subsidies.

At stake in the dispute are millions of dollars in future federal grant money for Wichita Mid-Continent Airport. Airports must agree to certain conditions to receive FAA grants for airport development. One of the conditions is that grant recipients not engage in “economic discrimination.” Doing so jeopardizes access to FAA grants.

The city has maintained that the airport and the city are separate entities, so the city’s subsidies should not affect the airport’s grants. The subsidies are paid with city tax money. The airport does not receive city taxes for support.

AirTran has received revenue guarantees from the city since it began business here May 8, 2002. The city offered $4.5 million for AirTran’s first two years of service and another $2.5 million for its third year.

City officials say keeping the discount carrier in Wichita helps reduce airfares, which they say are crucial to the city’s efforts to retain and attract companies.