SIPTU delegates have voted overwhelmingly to go into the next national wage talks at a special conference.
But the union's general secretary Joe O'Flynn said afterwards that these would probably be the toughest set of negotiations since the current generation of agreements began over 20 years ago.
Earlier, members of the country's largest union were told that workers are taking home less pay in real terms today than they were before the last national wage agreement.
But employers' group IBEC warned that pay could not chase inflation as this would place jobs at risk when the country was facing the biggest economic challenge for 20 years.
Towards 2016 awarded workers 10% over 27 months, but SIPTU's head of research Manus O'Riordan said inflation had more than eroded those increases.
Mr O'Riordan said the rate of inflation over the term of towards 2016 totalled 11.7%. As a result, he said that average workers were taking home 1.2% less in real terms than they were when Towards 2016 started. He said low paid workers had suffered an effective pay cut of 0.7%.
Mr. O'Riordan also said that pay for managers and senior staff was rising faster than that of production, transport and manual workers.
He warned that the union should not tolerate any attempt to amend the basis on which inflation was calculated that would exclude items like mortgage costs.
Proposing the motion to enter pay talks, SIPTU vice-president Brendan Hayes outlined the union's agenda for the talks, including pay increases ahead of inflation, equal treatment for agency workers, improved rights to union representation, better pension provision and the protection of public services.
Delegates voiced anger about calls for pay restraint at a time when senior politicians were receiving huge pay increases.
One delegate - Kieran Allen - said that workers should not have to carry the can for an economic downturn which had been caused by financial speculators who had treated the world like a global casino.
But IBEC director general Turlough O'Sullivan said Irish pay rates had been growing at twice the pace of those in other euro area countries, adding that this could not continue.
