The charges could compound cash-flow problems linked to a dispute with the DoH over an expected rise in the fee scale for dispensers (GP, 7 May).
The wholesaler, Alliance Healthcare, increased its minimum order level by £1,500.
From 1 May, the firm increased its 'low spend threshold' from £3,500 to £5,000 per order. For orders worth less than £5,000, dispensing practices are required to pay a £300 surcharge.
Dr David Baker, chairman of the Dispensing Doctors' Association, said some smaller practices across the UK will have difficulty reaching the required level to avoid a surcharge.
'If the order is just one packet of a product they might be clobbered with a surcharge. A 20p packet of aspirin might end up costing £300.20,' he said.
Dr Baker added: 'We are working with the wholesalers to try to alleviate the problem for smaller practices that genuinely cannot reach the minimum order required.'
A spokeswoman for Alliance Healthcare said the surcharge would not apply to practices which only order products from Alliance Healthcare as a result of an agency/distributor agreement.
But she said: 'Due to ever-increasing pressures in our sector, it has become necessary to introduce some amendments to our standard terms and conditions of sale. These changes bring Alliance Healthcare in line with other wholesalers.
'We recognise that some customers only purchase products from Alliance Healthcare where an agency or distributor agreements dictates and for those customers the low spend surcharge will not apply.'