Thousands of farmers could have to wait until mid-summer to receive outstanding GLAS and AEOS payments, the Irish Natura and Hill farmers Association (INHFA) has claimed.
Approximately 8,500 farmers have still to be paid under the environmental schemes, with close to €25m being owed in total.
But the Department of Agriculture is refusing to commit to a payments' timeframe for applicants.
A Department spokesperson told the Farming Independent that it is processing payment runs "at least on a weekly basis" and will continue to do so until "validated applications are cleared".
However, the INHFA claimed it would be June by the time all GLAS and AEOS farmers were paid given the current rate at which payments were being processed.
Vincent Roddy of the INHFA described attempts by the Department of Agriculture and Government ministers to blame the complexity of the scheme for the payment delays as "self-serving and insulting to farmers".
"The very idea that Department staff or Government ministers would blame the non-issuing of payments, on the fact that the GLAS scheme was very complicated, with a difficult array of over 30 measures, is truly shocking and ignores the fact that it was the Department themselves who designed an overcomplicated scheme," Mr Roddy said.
He accused the Department and Government ministers of "trying to pass over the blame for problems of their own making".
And more pressure is set to mount on Minister for Agriculture Michael Creed over the payment delays with Sinn Féin tabling a motion on the issue today at the Joint Oireachtas Committee on Agriculture, Food and the Marine.
The motion calls for all outstanding 85pc payments to be made immediately to 8,500 farmer applicants.
It is anticipated that the motion will be passed by the committee.
Minister Creed could opt to ignore the recommendations of the Oireachtas committee but such a move is likely to result in a Dáil motion calling for the immediate processing of outstanding payments.
Department officials have warned that the unilateral payment of all initial AEOS and GLAS applications (amounting to 85pc of the full payment) would be in contravention of EU rules as the necessary crosschecks would not be completed.
However, Sinn Féin and the farm organisations maintain that any future penalties or reductions to individual entitlements could be clawed back from the later 15pc balancing payments to farmers.
"I am very aware of the financial strain under which many farmers are operating and the excuses, justifications and muddying of the waters from the Department have served only to increase their frustration and stress," said Sinn Féin agriculture spokesman, Martin Kenny.