Farmers’ leaders have urged ministers not to bring in plans to cut subsidies by 15% and transfer cash to wildlife protection in England and Wales.
The National Farmers Union (NFU) has written to every MP, saying the plan to share £3.5bn of farm grants would disadvantage British farmers.
The NFU also warns MPs that going ahead with the move would risk rural votes.
The government said the money would help to build on the “success” of its environmental and rural growth schemes.
Wildlife groups have used newspaper advertisements to urge the government to keep its countryside commitments.
They also say votes are at stake as every household pays £400 a year to subsidise farmers – and people expect their money will be used to protect the environment, not just to shore up farmers’ budgets.
In the summer, the EU set the framework for how the money should be spent with its scheme to “green” the Common Agricultural Policy (CAP).
The greening plans were heavily diluted under pressure from farmers, but large landowners will in future need to do more to collect subsidies by leaving existing grassland unploughed, diversifying their crops and setting aside some land for wildlife.
What is being decided is exactly how the farm subsidy pot for in England and Wales should be divided between conflicting interests. The decision is tough because the overall size of the pot has shrunk as Europe’s leaders attempted to shrink the £50bn CAP.
The decision on the share-out is imminent.
In England and Wales ministers have indicated a wish to shift the maximum allowable – 15% – away from direct payments to farmers – which is mostly for owning farmland. The money will go towards protecting wildlife and stimulating the rural economy.
The NFU letter to MPs says this is unfair to farmers in England and Wales because farmers elsewhere are being better protected. In Scotland the government has decided to shift 9.5% of subsidies away from direct payments.
The NFU also complains that the government appears ready to transfer this amount without having decided the purpose of the transfer.
President Peter Kendall says in the letter to MPs: “Farmers remain at a complete loss to understand what the government intends to use this money on, and how it can be used effectively for the benefit of their businesses.
“The threat of disproportionate reductions in their payments vis a vis their immediate competitors is making them angry and frustrated with this government.”
Wildlife groups who take the opposite view believe Prime Minister David Cameron will be discussing the issue over the weekend.
The RSPB, which has registered huge losses in farmland birds through intensive subsidised farming, has taken a full-page advertisement in the Times warning: “This weekend the prime minister could cut the life from the English countryside.”
Green groups say public money spent on subsidising farmers should go on public good like thriving wildlife and well-managed water catchment areas to retain water for use and to prevent flooding.
A Defra spokesperson said: “Our environmental and rural growth schemes have delivered real benefits to the natural environment and rural economy.
“We want to build on these schemes’ success by channelling into them some of the money from the budget for farmers’ direct payments.
“We have sought views on the future of the Common Agricultural Policy in England and will make an announcement shortly.”
The final division will be complicated, with firms supporting rural development also hoping to benefit from the 15% transfer of funds.
In Scotland the government is consulting on plans to shift 9.5% of subsidies away from direct payments to farmers – a payment which is mostly for owning farmland. The money will go towards protecting wildlife and stimulating the rural economy