Fitzgerald said Thursday that the groups want to bolster public support for O'Hare expansion.
United spokesman Jeff Green says Fitzgerald's suggestion is "incredibly absurd." He says it costs the company $30 for every one minute of aircraft delay.
Chicago Aviation Commissioner John Roberson says the city does not need to manufacture excuses for new runways.
Fitzgerald supports a proposed south suburban airport. He wants Transportation Secretary Norman Mineta to restore delay controls at O'Hare that were phased out in 2002.
FAA statistics show delays at O'Hare have reached historic levels. In May, O'Hare set a monthly record of about 14,500 delays.