The European Commission has fined European and Japanese companies a total of 138.4m euros ($161m; £97m) for operating a price-fixing cartel in sorbates.
Monti criticised five firms for taking part in a "conspiracy"
Sorbates are one of the most widely used food preservatives in Europe to prevent the development of moulds, bacteria and other micro-organisms in food.
"Because of this conspiracy European consumers paid more for many everyday products than if the companies had competed against each other," Competition Commissioner Mario Monti told a news conference.
The largest fine, of 99m euros ($115m; £70m), was levied on Germany's Hoechst. The company has since merged with France's Rhone Poulenc to create Aventis, one of the world's largest drug manufacturers.
Other companies named in a statement included Daicel Chemical Industries, Ueno Fine Chemicals and The Nippon Synthetic Chemical Industry Company.
The Commission can fine companies up to 10% of their annual worldwide turnover for price-fixing offences.
However, Japan's Chisso Corporation which helped the EU head office gather evidence, was given immunity for cooperating in the probe.
The companies met twice a year to discuss setting prices for each country and allocating volume quotas for each other.
The EU executive said it had determined that the cartel ran between December 1978 and October 1996.
"I am determined that participation in a cartel should not pay," Mr Monti added.