Federated Farmers is concerned that cuts to the Official Cash Rate have not yet flowed through to interest rates on farm overdrafts.
A survey of federation members has found overdraft interest rates have fallen by 78 basis points between December - January, despite the OCR being cut by 150 basis points.
President Don Nicholson says banks should be giving customers better value and charging fairer interest rates.
Mr Nicholson says an interest rate of 8%, rather than 11%, would help keep the economy moving.
He says farmers hope any cut by the Reserve Bank to the OCR next Thursday, will quickly result in cuts to interest rates.
Westpac says farmers are benefiting from fixed lending rates, which are lower than the seasonal overdraft funding.
Its head of agribusiness, Dave Jones, says banks did their best to hold rates as long as possible when interest rates rose and are now trying to recover some of that margin.
He says less than 20% of loan balances are on floating interest rates.
The OCR is currently 5%. It has been lowered from 8.25% since last July.