The imposition of freight rate increases on Irish Sea routes from January has been described as "opportunistic" by the Irish Exporters' Association (IEA). Mr Colum MacDonnell, IEA chief executive, said he was considering referring the issue to the Competition Authority after members had been contacted by some freight companies alerting them to the new rates.

Irish Ferries, Stena Line and Pandoro, representing the vast majority of freight traffic, are increasing charges in the new year by amounts, according to Mr MacDonnell, ranging from 6 per cent to 10 per cent.

Mr Eamonn Hewitt, Stena Line communications manager, said investment costs of £250 million and tightening margins had made the increase necessary. "The margins have evaporated."

An Irish Ferries spokesman said an increase amounting to £30 for a typical articulated truck with a 40-foot trailer was being imposed because of investment costs.