How should we handle mandatory overtime when determining FMLA leave hours?

Q. Can an employer deduct or count overtime hours from an employee’s FMLA balance? Our employees work overtime only from October through December. During that time, they’re required to work 12-hour days, seven days a week. We have several employees on both continuous FMLA and intermittent leave, and we’d like to deduct the overtime hours they would have worked from their FMLA allotment. What do you think?