My Coworkers are Taking Advantage of the System

Dear Evil HR Lady,

My supervisor has about 1/3 of his large staff (50+) on Family Medical Leave (FMLA). They use it intermittently, which means that they are not out for weeks at a time, but, rather, take what time they need when they need it.

For the majority, when any of them call in, it is always on a Friday or a Monday and it happens over and over, but nothing is ever done about it. In particular, I have one coworker whose abuse of FMLA and complete arrogance towards any rules goes beyond comprehension. He arrives at work late, then stands around and chats with the people for 15, 20, or even 30 minutes or longer before he starts any work. Other times, he will make it look like he's working and continue to talk, talk, talk, but management rarely says anything to him. He frequently leaves the floor and has been caught watching television and eating when he should be working.

So, what do you do when your coworkers are taking advantage of the system?