The Government must raise personal and PAYE tax allowances by at least £2,300 in the Budget to honour commitments to workers, according to the SIPTU president, Mr Des Geraghty.
He has also warned the Government and employers that the economic slowdown "provides no excuse whatsoever" to "pull back" on commitments in the Programme for Prosperity and Fairness.
At the opening of the biennial conference in Tralee yesterday, Mr Geraghty said: "SIPTU will not accept any 'hard landing', paid for once again by the poorest, most vulnerable and most expendable lower-paid workers and their families, while stockbroker economists lecture us about social responsibility or market realities.
"Equally, we do not accept that there is any basis for reneging on the key tax commitments made to us in the PPF. The days of the poor paying for the extravagances of the rich are over."
The remaining pay and tax provisions of the PPF "must now be delivered in full".
Mr Geraghty continued: "The fact that Ireland's growth last year was twice the average envisaged under the programme, and that it was on a par with it this year, means that growth over the full period of the PPF will still match the projected average annual GNP increase of 5.6 per cent provided for in the programme.
"Certain tax cuts are indeed undesirable, in particular the PD obsession with cutting the top rate of tax from 42 per cent to 40 per cent. But the PPF commitment to take all those on the minimum wage completely out of the tax net must definitely be met and will have a beneficial effect on our economy."
The Tβnaiste, Ms Harney, had promised "unequivocally'" to take people on the minimum wage out of the tax net, Mr Geraghty said, quoting from a Department of Finance document on Budget 2001.
This could be done with an increase of £2,300 in allowances next January, but with the increase in the minimum wage to £5 an hour from next October, it will need a further upward adjustment of £600 a year to meet Government commitments.
Defending the PPF from critics within the trade union movement' Mr Geraghty said: "Some of the achievements, and unfortunately some of the things we did not achieve, carry far more significance for the future of workers than whether we got 1 per cent, 2 per cent or 3 per cent more than inflation, or more than was expected.
For a worker with a large family, for example, a £7, £8 or £10 increase in the monthly Child Benefit - especially as it's not taxable - may be worth far more than a taxable pay increase of just a few percentage points.
"For a young couple struggling to pay a huge mortgage or saving up for one . . . the introduction of tax relief on childcare would put more disposable income into their pockets than a general, across-the-board and relatively small pay increase."
In the long term, "what will matter most for our members is the pay level at which they retire and the size and adequacy of their retirement income."
Training and education were vital to improving workers' earning power.