Strikes at two Tesco stores could spread to at least 20 other branches in the new year following three stoppages ahead of Christmas.

Pickets will be mounted at a branch in Co Sligo today and on Friday week, followed by a strike in Carrick-on-Shannon on December 22.

Mandate, which represents more than 8,500 staff, said it was assessing “outstanding issues” at a minimum of 20 other stores.

“There is real potential for this to escalate,” said assistant general secretary Gerry Light. “This is something that’s been waiting to happen for the last three years.”

He accused the company of “de-recognition” – refusing to engage with the union on staff issues including security bag checks and changes to canteen facilities. Mr Light said the parties were given four dates at Workplace Relations Commission but the company refused to attend.

A Tesco spokesperson said stores would remain open during the “unwarranted” strikes. She claimed the union was in breach of agreed procedures.