The European Commission has proposed cutting direct subsidies to farmers while increasing the share of funds going to smaller farms.
The changes to the Common Agriculture Policy have been described as a major threat to farming in Ireland by the Irish Farmers' Association, and have also attracted criticism from France and other countries that benefit most from EU agriculture aid.
Under plans for the EU's budget for 2021-2027, farmers would receive around €232 billion in direct support, a drop of more than €30bn from the current seven-year budget.
The Commission proposed giving more money to small farms and recommended member states set aside at least 2% of their direct agriculture funds from the EU for young farmers, but acknowledged that this could encourage larger farms to simply split up.
"Nobody stops farmers from splitting the farms," Agriculture Commissioner Phil Hogan told a news conference.
The agriculture ministers of Ireland, France, Spain, Portugal, Finland and Greece have issued a joint statement saying they oppose the proposed cuts - which must be approved by all 27 EU members - and called for maintaining current spending levels.
In a statement, the IFA said: "It is completely unacceptable that any cut is being contemplated when farmers are already struggling on low incomes."
The organisation has called on Taoiseach Leo Varadkar to oppose the planned changes.
Direct payments to farmers would still form the bulk of EU agriculture spending, or one fifth of all EU expenditure in the planned €1.1-trillion long-term budget.
As part of a wider policy to divert some EU money to new sectors, like research and security, most EU countries would see a drop in direct aid to their farmers, except the Baltic countries and other smaller eastern EU states who would see their funding increase.