Fitness for duty exams are not popular with the workforce.  They can be very stigmatizing.  But, employers want to know if an employee has issues that could affect business.  Most caselaw says fitness for duty exams for unspecified reasons are not justified – they are perceived s a backdoor to discriminate based on disability.  But, the 9h Circuit found in Brownfield v. City of Yakima that sometimes they are appropiate.  See decision.  In this case, a police officer exhibited erratic behavior a few years after he sustained a head injury.  He was complaining over a period of years about a supervisor who Brownfield believed was keeping him from  promotion.  After exhibiting some erratic behavior, his employer required him to see a doctor and provide a report.  Brownfield cooperated at first and then refused to follow through.  The first doctor did find a mental diagnosis.  

The court found that in a workplace where the employer is engaged in dangerous work, preventive fitness for duty exams might be appropriate where there is a business necessity.  The court cautioned that they should not be used as a means to harass an employee or to fish for non-work related medical issues.  The business necessity standard is "quite high" and should not be confused with mere expediency, said the court.  The court then concluded: 

         "Nevertheless, we hold that the business necessity standard
         may be met even before an employee’s work performance
         declines if the employer is faced with significant evidence
         that could cause a reasonable person to inquire as to whether
         an employee is still capable of performing his job. An employee’s
          behavior cannot be merely annoying or inefficient to
         justify an examination; rather, there must be genuine
         reason to doubt whether that employee can perform
         job-related functions."

This ruling may not provide the clearest guidance, but it is a start.