The probe includes European and Italian paper packaging companies and the industry association GIFCO, for alleged price fixing and market manipulation between 2015 and 2016.
The companies under investigation include DS Smith Packaging Italia and its affiliated company Toscana Ondulati, Smurfit Kappa Italia, International Paper Italia, Pro-Gest and its subsidiary Cartonstrong, Ondulati Nordest, Ondulati ed Imballaggi del Friuli, Sada Partecipazioni and its group companies Antonio Sada & Figli and Sada Packaging, Innova Group, Laveggia and its subsidiary Scatolificio la Veggia, and Imballaggi Piemontesi.
AGCM claims the companies were involved in an alleged corrugated cartel and agreed on fixed prices and the quality and variety of products sold to independent corrugated packaging manufacturers by using an informal price list called Listino GIFCO, Listino Toscano or Listino 2004.
It said the companies had allocated customers and were sharing sensitive information on product characteristics and production volumes.
AGCM said it searched the premises of several companies involved in the case last month (March 30) with Italy's Guardia di Finanza (Special Unit Antitrust Financial Police).
In response to the accusations, DS Smith, International Paper and Pro-Gest confirmed AGCM and Guardia di Finanza had carried out antitrust inspections on its premises in Italy and it was fully cooperating with authorities on the matter.
Ondulati ed Imballaggi del Friuli said it had not been subject to an inspection but was informed about the investigation via email and also offered its full cooperation.
According to AGCM, the investigation falls under Article 101 of the Treaty on the Functioning of the European Union, which prohibits cartels and other agreements that could disrupt free competition in the European Economic internal market.
It states businesses infringing the provisions of Article 101 are liable to unlimited fines by the European Commission, but the EU has no authority to impose prison sentences.
It prohibits any agreements between businesses which may affect trade between Member States and which effect the prevention, restriction or distortion of competition within the internal market.
AGCM claims the market value of corrugated packaging in Europe is approximately €20bn ($21bn) and Italy is the second largest European producer after Germany.
"The production of corrugated cardboard has registered in recent years a strong positive trend, even in the face of the difficult economic situation which has characterized the period. This appears due to the increasing popularity of online commerce and the increasingly widespread use of such packaging in the food industry," the association said in a statement.
"The preliminary hypothesis concerns the existence of two autonomous arrangements among the main domestic manufacturers of corrugated cardboard and corrugated cardboard packaging, relating to the coordination of the commercial conditions in the markets of corrugated cardboard and retail sales of packaging, with reference to their sales prices, the level of discounts, as well as the allocation of customers."