United, American reportedly have growing concern with O'Hare Airport expansion costs

CHICAGO (CBS)-- The two largest carriers at O'Hare Airport are growing concerned with the cost of the airport's massive, multi-phase renovation plan.

City Council Aviation committee chairman Matt O'Shea told the Chicago Sun-Times that both American and United have been engaged in high-stakes negotiations on the renovation plans for "months"  with a meeting between both airlines and the mayor's office held on Monday.

O'Shea also claimed that United has revived a 2018 threat to move its headquarters from Chicago if it doesn't get its way.

Those airlines say the enormous next phase of the expansion project, which will build a new terminal to replace  Terminal 2 is already 24% over budget.

The renovations are funded by airline ticket taxes and landing fees, which is the main cause for American and United's concerns.