A Sydney wholefoods store has been criticised by the Fair Work Commission for its "extraordinarily heartless" treatment of a chef it dismissed after he was absent for three days for cancer treatment.

Urban Orchard Food in Sydney's Circular Quay gave chef Chanintorn Siri three days' sick leave when he was admitted to hospital with severe stomach pain related to his pancreatic cancer, but phoned to summarily dismiss him two days later, according to a commission judgment released on Tuesday.

A chef at a Sydney wholefoods store was summarily dismissed.

The judgment said Urban Orchard's owner Gabrielle Levette had told Mr Siri he was an unreliable employee and that she had offered his job to another cook.

She argued Urban Orchard had complied with the Small Business Fair Dismissal Code because it had "reasonable grounds" to believe Mr Siri engaged in ongoing conduct of fraudulently completing his timesheet.