FMLA: Who is considered a ‘key employee’?

Q. On the U.S. Department of Labor’s Form WH-381 “Employer’s Response to Employee,” there is a line that asks whether the worker is a “key employee” as described in the FMLA regulations. I always check the box indicating that the worker is a key employee. How should I mark these boxes? I consider most of our workers key employees, and I do not want to offend anyone by suggesting that they are not.