CHICAGO (CBS)– A Red Robin restaurant in Orland Park closed Friday night after a Carbon Monoxide leak sent four to the hospital, according to the Orland Fire Protection District.

About two dozen customers started to feel sick and complain of headaches when Orland Fire officials arrived at the Red Robin, located at 1502 S. LaGrange Rd.

After testing, officials say high levels of Carbon Monoxide were detected and the HVAC units were causing the problem.

The restaurant will remain closed until repairs are complete.