Car parts to bicycle retailer Halfords has been accused of bullying small firms and abusing its market dominance by a imposing a unilateral price cut on suppliers.
The Forum for Private Businesses has written to Trade and Industry Secretary Alan Johnson to complain about the behaviour of the Worcestershire firm.
The FPB criticised Halfords for unilaterally imposing a five per cent reduction on all products and attacked the new terms as "a kick in the teeth to suppliers".
It said the Redditch company had also imposed a 2.5 per cent increase in retrospective rebates - a discount on goods already bought, while increasing the time it had to pay for products from 60 to 80 days to 120.
One Halfords supplier told the FPB: "Unlike in the food sector where there is a code of practice policing the relationship between suppliers and supermarkets, in our sector suppliers are unprotected and vulnerable.
"Halfords is abusing its total market dominance, as the only retail giant in the sector, and is wringing the money out its suppliers. It is all about greed.
"There is no loyalty, especially since Halfords left the Boots group. These new payment terms will endanger businesses and will cause job losses."
Nick Goulding, chief executive of the FPB, said: "Halfords must not and cannot be allowed to abuse its market dominance, without fear of challenge or punishment.
"The Government must intervene in this matter to ensure the interests of Halfords' suppliers are not ridden rough shod over.
"We have written to Halfords' chief executive telling him that these unilateral changes to payment terms - imposed mid-contract without negotiation - are contrary to UK and European late payment legislation."
A spokesman for Halfords declined to reveal the change in its supplier contracts, and dismissed the action by the FPB.
He said: "This is a publicity stunt. We are not negotiating with our suppliers in public via a third party.
"We are growing and successful business. We create a lot of jobs in the Midlands and we want suppliers to join in with us.
"We talk to and negotiate with our suppliers all the time, and if any suppliers had any issue they should take them up with us.
"I don't think these complaints are representative of our suppliers." n The FPB has called for an inquiry by the Competition Commission in to the behaviour of Tesco.
Mr Goulding raised concerns about the increasing High Street dominance of the chain.