Can we search an employee’s car if we think she’s using drugs at work?

Q. We suspect an employee has been getting high at work. Over the past two weeks, co-workers have reported that the employee’s pupils were dilated and her speech was slurred. She stares out the window for extended periods of time, she fell while walking down the hall, her appearance is disheveled, and she takes multiple “rest breaks” to go to her car throughout the day. We want to search the employee’s car, but she refuses to let us. Can we search her car anyway? ...