More than 100 Sobeys workers in Kincardine voted last night to join Unifor.
It's Canada's largest union in the private sector.
The new bargaining unit includes full-time and part-time workers, as well as students.
According to a release by Unifor, the Sobeys supermarket chain, owned by Nova-Scotia based Empire Company Limited, is Canada's third largest grocery retailer, generating more than $6-billion in food sales last year.
Unifor represents more than 310,000 workers, including 20,000 retail workers across Canada.
