The Irish National Teachers' Organisation has demanded that the Government fully restore the primary school capitation grant to the 2010/11 levels of €200 per pupil.
The grants cover the day-to-day running costs like heating, lighting, insurance, general upkeep and the purchase of teaching materials.
Speaking on RTÉ's Morning Ireland, INTO General Secretary John Boyle said a cash injection is needed in primary school education if the Government wishes to prioritise the future of early years education.
Mr Boyle said primary schools are being "impoverished" by the current capitation grant of €170 per child - which is set to increase to €179 per pupil from September.
This increase will bring schools back to the level of funding they were receiving in 2007/08.
Mr Boyle said the increase was "already spent" due to rising insurance and energy costs and is only a "plaster on the wound".
He said the grant should be further increased to put it on a par with the grant given to secondary school students, which is approximately €309 per pupil and set to increase by €15 per student from September.
Mr Boyle said a 20% increase for the following four years would put primary schools on parity with post-primary schools and, that for the last eight years, parents have been making up shortfalls by paying voluntary contributions.
Mr Boyle said the latest OECD report on education funding states that average investment in education was 5% across developed countries, it fell to 3.5% in Ireland, and the funding given puts Ireland "at the bottom half" of the OECD countries.
Since 2010 capitation has been cut by 15%, from €200 per child a year at primary level to €170.
The Society of St Vincent de Paul said last summer that the number of parents contacting it for help with back-to-school costs had increased by 20%.
Minister for Finance Paschal Donohoe announced a 6.7% increase for education last October's Budget.