The companies make and distribute polystyrene foam trays and polypropylene rigid trays widely used for packaging such food products in the European Economic Area.
The EC has sent an official statement of objections to these businesses, the identity of which it has not disclosed.
It claims they may have engaged in price fixing, market sharing, customer allocation, exchanges of commercially sensitive information and bid-rigging.
If true, this would constitute a breach of Article 101 of the Treaty on the Functioning of the European Union (TFEU) that prohibits cartels and restrictive, anti-competitive business practices.
In addition, the firms in question each face fines of up to 10% of their annual worldwide turnover if any case against them is proven.
The EC said such practices, if established, may have affected direct customers, such as supermarkets, and ultimately consumers.
Under the terms of the law, the companies to which the EC has written can now examine the documents on its investigation file and reply in writing.
They can also request an oral hearing to present their comments on the case before EC representatives and national competition authorities.
Cartel investigations vary in duration according to the complexity of the case, the number of markets and companies involved and the extent to which accused firms cooperate with the EC.
The EC declined to comment further at this stage, after issuing a general statement about the investigation.