A telephone company worker got married on a day she was supposed to use approved medical leave for migraines. Another employee, who took leave because of an anxiety disorder, played drums in a band on the Fourth of July. A flight paramedic attended three air shows over 12 weeks of baby-bonding leave.

All of these workers were fired for misusing leave. All accused their employers of violating the Family and Medical Leave Act. And they all lost in court.

That’s...