A round of drinks turned into a medical nightmare when three customers ordered margaritas and immediately suffered chemical burns inside and around their mouths.

Health officials investigating the incident at a Chili's Grill & Bar in Forest City, North Carolina, said the drinks were contaminated after a powerful industrial degreaser was mistaken for sugar.

The dangerous mix-up began when a restaurant worker obtained granulated degreasing agent from an outside contractor power-washing the building's exterior, according to the Foothills Health District.