SIPTU members are due to begin voting today on whether to accept or reject the new national pay deal negotiated earlier this year.
Around 250,000 of the union's members are eligible to vote on the matter over the next three weeks.
Yesterday, the SIPTU leadership recommended a vote in favour of the agreement, despite major concerns about the 1% income levy introduced by the Government in last week's budget.
SIPTU also has concerns about the cutbacks in health and education announced by Finance Minister Brian Lenihan and is vowing to campaign against them.
However, it says voting against the pay deal would do nothing to reverse those cuts.