The U.S. Supreme Court case Northwest Airlines, Inc., et al. v. County of Kent, Michigan, et al., 1993 revolved around the issue of whether airport user fees imposed by a county violated federal law or were preempted by it. The airlines argued that the fees charged for use of facilities at Gerald R Ford International Airport in Grand Rapids exceeded what was reasonable and thus contravened with Federal Aviation Act's prohibition on excessive charges and unjust discrimination against air carriers using similar services provided under comparable conditions at other airports across the country. However, the court ruled in favor of Kent County stating that these user fees did not violate any federal laws nor were they preempted by them as long as they adhered to certain standards set forth by Secretary of Transportation regarding reasonableness and nondiscrimination among users. This decision affirmed that local governments have some discretion over setting rates for their public utilities including airports while also emphasizing that such powers should be exercised within limits established under federal law to prevent unreasonable or discriminatory practices.

In the dissenting opinion for Northwest Airlines, Inc., et al. v. County of Kent, Michigan, et al., Justice Scalia disagreed with the majority's interpretation of federal law and its application to this case. He argued that the Airport and Airway Improvement Act (AAIA) does not permit airlines to challenge airport fees under a reasonableness standard unless there is an express agreement between them and the airport operator regarding those fees. In his view, AAIA only allows such challenges if they are based on allegations of unjust discrimination or violations of written assurances provided by airports as conditions for receiving federal grants. Furthermore, he contended that even if AAIA did allow airlines to challenge fee reasonableness in court without an explicit agreement about those fees with airports, it would still require them to exhaust administrative remedies before filing lawsuits - something which Northwest Airlines failed to do in this case.