TESCO customers may have to pass pickets to do the weekly shop as the supermarket faces the threat of a national strike.
Thousands of workers at almost 30 stores have begun balloting for industrial action that may escalate to the British retailer's 116 stores in the Republic.
The biggest union at the chain, Mandate, has decided to begin a ballot at over 20 stores where staff have had their hours cut by up to 10 a week. SIPTU announced last week that it would ballot staff at six stores.
SIPTU National Industrial Secretary Gerry McCormack said a national strike may follow if the chain -- which has 13,500 workers -- does not row back on the reduced working weeks.
He said there was no justification for the cost-cutting measures as Tesco had a €250m profit in the Republic in the past year.
The union has accused the chain of breaching an agreement that it could not cut hours unless there was a major drop in trade.
Workers at around 30 Tesco branches have suffered a major reduction in their hours, including staff at Portlaoise, Edenderry and Mullingar.
Tesco said it was within its agreement with the unions to reduce hours.
"Working hours in a number of stores have been adjusted to reflect changes in day-to-day trading patterns," said a spokesperson.