The organisation representing primary school principals claims the Government is providing just half the money needed by schools to cover day-to-day running costs.
The Irish Primary Principals Network says a survey it carried out in 200 primary schools found that the average capitation grant was €25,000 per annum, compared to running costs of €48,000.
The organisation says just 3% of schools are receiving enough government money to meet their basic costs like light, heat, insurance, cleaning and the purchase of supplies.
Eight per cent of the schools surveyed were found to be relying on fundraising from parents to cover the shortfall.
The IPPN is calling for an independent analysis of schools' operating costs to determine appropriate the level of capitation grants, which it also says should be paid on a monthly basis.