SIPTU has accused Tesco Ireland of walking away from pay talks with the union and instead unilaterally introducing changes to workers' pay and conditions.
The company also announced an increase in paid maternity, adoptive and paternity leave.
SIPTU said that its representatives put forward proposals concerning a new pay agreement to management at a recent meeting but that these were ignored.
"This is a retrograde step by the company and will result in a response by SIPTU members," said SIPTU Sector Organiser Denis Sheridan.
"The SIPTU Tesco National Committee will meet in the coming days to consider all options open to it as a consequence of this unacceptable development," Mr Sheridan said.
SIPTU Tesco Shop Steward Catherine Smith said that the staff she represents were disappointed by the move.
"This is a very damaging development for relations between staff and management in the company," Ms Smith said.
In a statement, Tesco Ireland said that over the past 12 months, it engaged in agreed independently-mediated discussions with staff representatives and their trade unions to try to agree a new model of engagement that would provide for timely and definitive outcomes where any proposed changes, including pay, would benefit from negotiations.
"Unfortunately, we were unable to reach a shared view through that mediation process, but we continue to remain open to reengaging with the trade unions in the future should they have constructive proposals on how such a model can be achieved," the company said.
