A transportation agency accuses United Airlines of falsely claiming to buy jet fuel out of a small office in a rural Illinois community to avoid paying tens of millions of dollars in taxes in Chicago, where the purchases are allegedly being made.

The Regional Transportation Authority says it will file a lawsuit Monday alleging that United Airlines subsidy United Aviation Fuels is operating a "sham" office in Sycamore.

The RTA says United Aviation Fuels reached an agreement to pay the DeKalb County community at least $300,000 a year. That's far less than it would pay Chicago and Cook County in sales taxes.

The RTA alleges American Airlines is doing the same thing in Sycamore but isn't suing because American is in bankruptcy.

Both airlines say the Sycamore operation is legal.