The Fair Trade Commission plans to fine some 60 cardboard makers around ¥13 billion over an alleged cartel, sources said Thursday.

Among them, Tomoku Co., Oji Container Co. and Nippon Tokan Package Co., all based in Tokyo, have already received drafts of punishment notifications from the anti-monopoly watchdog, they said.

The FTC will fix the punishment after hearing the opinions of the companies, including Osaka-based Rengo Co., the nation's largest cardboard maker, they said.

The watchdog raided the companies over the alleged cartel in June and September 2012.

The companies started collaborating on fixing price hikes for cardboard boxes sold to large customers, including beverage and appliance makers, several years ago, the sources said.

It might have been designed to avoid a price-cutting war and secure profit margins in the face of rising production costs in the industry, they said.

The FTC had repeatedly warned the cardboard industry to stop colluding on prices.