THE Ulster Farmers' Union (UFU) has complained that renewable heat incentive claimants have been hit by the continued impasse at Stormont.
The union said it was "frustrated" by the response it has received over plans to extend revised RHI tariffs.
The botched green energy scheme, which effectively paid claimants to burn more fuel than they needed, was expected to have an overspend of up to £490 million.
In January, then economy minister Simon Hamilton announced proposals to tackle the bill, including imposing a one-year, two-tier tariff structure and payment cap from April 1.
The DUP minister's proposals, which were passed by the assembly, prompted a legal challenge which is to be heard in October.
The UFU wrote to the Department for the Economy's (DfE) permanent secretary, Andrew McCormick, to express its concerns over proposals to extend the temporary tariffs.
Chief executive Wesley Aston said the plans could hit the finances of farm businesses enrolled in the RHI scheme.
"The permanent secretary has confirmed that while the revised tariff extension remains a proposal from DfE, he has clarified that it can only proceed with the return and approval from a government minister," he said.
Mr Aston said boiler owners feared temporary tariffs could be in place for longer than they expect.
"Many farmers have made long term investments in a government-backed programme and it is wholly unacceptable they should have to bear the financial burden due to the ongoing uncertainty at Stormont," he said.
The UFU also called for a full audit of all RHI boilers to be set up as soon as possible.
