The Ulster Farmer's Union (UFU) has said it is "bewildered and frustrated" by a proposed tariff increase to the RHI scheme in Northern Ireland.
Tariffs were slashed in the wake of the original botched green energy scheme after it was revealed the government was handing out subsidies so high that it paid users to burn wood pellets.
The "cash for ash" scandal led to the collapse of the Stormont Executive in 2017.
An independent review of the tariffs has recommended increasing the medium biomass tariffs in order to achieve "the appropriate return on investment".
However, the UFU said the increase was "insubstantial" and would not benefit struggling boiler owners.
UFU deputy president Victor Chestnutt said: "The Department for Economy (DfE) are proposing a poor tariff increase from 1.8p to 2.5p for 20-99kW boilers and a meagre 0.1p rise for 100-199kW connections.
“The tariff increase that has been proposed by DfE doesn’t even come close to what the UFU called for last month. We sought for the reinstatement of a tariff structure that is reflective of the true costs associated with running a boiler.
"What is even more confusing is that the recommendation comes on the back of a report by Cornwall Insight which recognised a rise in fuel prices as well as boiler service and maintenance costs.
We want to see the full reinstatement of a fair tariff that reflects their costs. It is a very reasonable request and the least boiler operators deserve at this late stage.UFU vice president Victor Chesnutt
"Yet DfE have only increased one tariff by 0.7p and the other by 0.1p which could result in many boiler operators moving to oil centred heating especially with the current price of oil."
The review was tasked with looking into hardship experienced by participants on the scheme after tariffs were slashed.
This came after it was discovered the scheme was creating a "perverse incentive" for boiler owners to burn fuel.
An inquiry into the scheme found "corrupt or malicious activity" on the part of officials, ministers or special advisers was "not the cause of went wrong with the NI RHI scheme.
Rather it was an accumulation of errors, omissions over time and a failure of attention, of those involved.
“UFU boiler operators invested in the RHI scheme in good faith only to be sold out and the UFU’s position remains unchanged," Mr Chesnutt added.
"We want to see the full reinstatement of a fair tariff that reflects their costs. It is a very reasonable request and the least boiler operators deserve at this late stage."
Mr Chesnutt said there is a shortage of biomass on the back of the coronavirus lockdown.
He added: "There have been moves in Great Britain to extend their RHI scheme meanwhile in Northern Ireland, our Government continue to offer our members mere crumbs from the table."
Announcing the move, Economy Minister Diane Dodds said: "I have made it clear that, in relation to matters involving the RHI Scheme, I will always seek to act in a manner that is fair to both scheme participants who joined in good faith and to taxpayers who are funding the scheme."
A DfE spokesperson said: “The consultation on tariffs is based on independent, expert analysis of the costs faced by RHI participants in Northern Ireland. The Department will consider all evidence put forward by the UFU and other stakeholders during this consultation period which will help inform the Executive’s decision on RHI tariffs.”