In United Private Detective & Security Ass'n v. City of Chicago, 56 Ill. App. 3d 242, 244, 371 N.E.2d 1087, 14 Ill. Dec. 34 (1977), the plaintiffs, private detectives and agencies, sought to recover license fees, alleging that they were illegally collected under an invalid city ordinance. The appellate court held that the trial court did not err in finding that the plaintiffs' complaint sufficiently stated facts warranting a finding that the payments for the licenses were made under duress, where the "plaintiffs alleged that the controlling motive for the payment of fees was the desire to avoid adverse economic consequences imposed by an ordinance they believed to be invalid." United Private Detective, 56 Ill. App. 3d at 245. The court noted that, although the plaintiffs did not file a formal protest, two days after the fees were paid they filed suit in federal court to have the ordinance declared unconstitutional. United Private Detective, 56 Ill. App. 3d at 245.