UK farmers could face severe financial problems because the government has overpaid £20m in subsidies and now wants the money back, their union says.
Some farmers are still owed money due last December, the NFU says
The National Farmers' Union (NFU) says the government has "reacted incredibly quickly" in asking for the money back.
But it complains some farmers are still owed money due last December.
The government says the overpayments are due to administrative blunders. It says its "main task" is to pay out money still owed as soon as possible.
The Rural Payments Agency (RPA) has paid about 500 farmers £30,000 each too much, while about 800 have been overpaid by £7,000.
The agency was set up to administer a new European subsidy scheme to make sure British farmers get the support they are entitled to.
The RPA has also been tasked with digitally mapping all of the UK's fields 2.5 million fields.
NFU president Peter Kendle told BBC News that the union wanted swift action on money still owed.
"They've put enormous amounts of resources into remedying the overpayments and they have reacted incredibly quickly, once they realised what had gone on," he said.
"I want them to show the same speed and commitment to getting the rest of the farmers' money out.
"Now, we've got another year coming round and the rest of Europe will be receiving their money in about four months time. We're not on track to meet those targets either."
Farming Minister Geoff Rooker said overpayments had been made to about 1% of the UK's 110,000 farmers.
He said he could not "explain which key was pressed to send an overpayment".
"We regret this, it is EU money - originally British taxpayers' money - and the auditors will require that we get it back," he added.
"But out main task, at the present time, is to make sure we pay the rest of the money we owe to farmers this year."
Up to 6,000 farmers were still owed amounts under 1,000 euros (about £700), Mr Rooker said.
"We've still got about 200 farmers that we owe over 1,000 euros to, some of which are quite complicated cases, because of either liquidation or probate, so there's a complicated issue at the end."
A change in the way farmers were paid subsidies had caused problems, he said.
The new subsidy gives farmers a single sum irrespective of how much food they produce.
"The Rural Payments Agency is doing a hell of a good job. It pays out 42 different subsidy schemes.
"And the single farm payment replaced 11 separate payments to farmers when we paid them to produce food."
When the new system had "bedded down", which would take "a couple of years", and all the fields had been digitally mapped, there would be "a smoother system", he said.
"It will be a lot, lot, better than the previous scheme when we paid farmers, in some cases, to overproduce food."