How do you ask for proof? Just ask. Get a doctor's note on the doctor's stationery. This alleged condition essentially means that this employee is only intending to work a four-day week for the next . . . one to two years. Can your business afford to pay her full-time for less than full-time work? As an employer with only 10 employees, you do not meet the thresholds where the federal employment laws would apply.
You may have a number of options at your disposal. You may be able to fire her, reduce her salary or work out a telecommuting arrangement where she works from home on the weekend (to make up for the Friday she'll be missing. Speak to a local employment attorney to determine your options under federal and state law.
Nina L. Kaufman, Esq. is an award-winning New York City attorney, edutainer and author. Under her Ask The Business Lawyer brand, she reaches thousands of entrepreneurs and small business owners with her legal services, professional speaking, information products, and LexAppeal weekly ezine. She also writes the Making It Legal blog.