Employees must give their employers 30 days’ notice that they will need FMLA leave. If the employer requests medical documentation and/or medical proof of the need to take off work, that documentation must be provided to the employer within 15 days of the date the leave will start. Despite these time requirements, there are provisions in the law dealing with unplanned emergencies and the need to take FMLA. You can take emergency FMLA leave, but you should inform your employer as soon as possible once the need arises.