Public Health Wales said those affected by the diarrhoea and vomiting outbreak had been to Hi-Tide in Porthcawl, Bridgend county.
The outbreak has been linked to the bar and health officials are trying to find the source along with which bug has caused the illness.
A statement from the bar said it was cooperating with the investigation.
"We would like to reassure customers that we take health and hygiene issues very seriously and monitor food preparation in line with industry standards."
A bar is being investigated after about 50 people who attended private functions there fell ill.