SYCAMORE – Sycamore could lose millions in a lawsuit filed Monday by the Regional Transportation Authority claiming a sales-tax agreement the city has with United Airlines is improperly diverting tax money from the RTA and Cook County.

Sycamore and United Aviation Fuels Corp. are in the 11th year of a sales-tax agreement that allows United Airlines to use Sycamore office space to conduct fuel purchases and avoid the 9.5 percent Cook County sales tax.

Instead, United Airlines benefits from Sycamore’s 8 percent sales tax and a generous rebate from the city.