Handle that search as unobtrusively as possible. You’ll make it less likely for the employee to sue for invasion of privacy and win.
Recent case: Philip Morris manager Robin Curry was suspended for allegedly violating company rules for handling subordinates’ leave requests. The company called her in for a meeting at which she would be terminated. When she arrived in the parking lot, security staff searched her car.
She sued, alleging invasion of privacy. But the court said the search wasn’t something that would have been highly offensive to a reasonable person. (Curry v. Philip Morris, No. 3:08-CV-609, WD NC, 2010)