Contract talks were set to resume Tuesday for about 2,000 Safeway and FreshCo workers across Manitoba.
The United Food and Commercial Workers Local 832, which represents the workers, says the current collective agreement expires on March 19.
The union says negotiations with the grocery chains, which are both owned by Sobeys, have not gone well.
It says more than 98% of workers who voted over the weekend were in favour of a strike mandate.
Sobeys says talks with the union began in December and the company is committed to finding a deal that respects the workers and keeps business competitive in the province.
The company says it remains committed to the bargaining process.
"We know that if we work together, we can find common ground," Sarah Dawson, Sobeys public affairs lead, said in an emailed statement.
The union says it represents employees at grocery stores in Winnipeg, Brandon, Thompson, Neepawa and Dauphin.
"Sobeys Capital Incorporated has consistently called its employees heroes, but it's time for them to move beyond words and show their gratitude in a more meaningful way," Jeff Traeger, the union's president and lead negotiator, said in a new release.