Working Overtime Can Be Essential Job Function- SHRM The ability to work overtime can be an essential job function under the Americans with Disabilities Act (ADA), the 8th U.S. Circuit Court of Appeals ruled, deferring to United Parcel Service's (UPS's) explanation that overtime was essential given unpredictable increases in workload, such as during the holidays and inclement weather. The plaintiff worked for UPS as a delivery driver for more than 30 years. After multiple physical ailments due to a back injury and a degenerative hip condition, his doctor determined that he was unable to work more than eight hours per day. UPS, however, required delivery delivers to be available for overtime work, up to 9.5-hour days. When the plaintiff informed his manager of his work limitation, his manager allegedly told him, "Congratulations. Your career at UPS is now over. … UPS won't allow anybody to work with a permanent restriction."