BRUSSELS (AFP) - The EU's competition watchdog fined five European envelope makers 20 million euros (S$32.65 million) on Thursday for drawing up a price-fixing cartel.

Competition Commissioner Margrethe Vestager told reporters the issue would "not only interest me but anyone who is writing Christmas cards."

"On this case we have closed the envelope, sealed it and returned it to the sender with a clear message: don't cheat your customers, don't cartelise," she said.

France's Hamelin received the biggest fine of almost 5 million euros in the case, followed closely by Germany's Mayer-Kuvert and Spain's Tompla.

GPV of France and Sweden's Bong were also fined.

Senior managers orchestrated the cartel in secret meetings often passed off as "golf and mini-golf outings", Vestager added.

The European Commission, the EU's executive arm, opened the case in 2010 based on a tip by an anonymous whistleblower. The cartel operated between 2003 and 2008.

The penalties were however reduced by at least 10 percent after the companies acknowledged responsibility and in some cases cooperated in the investigation.

The case marks a departure from the EU's recent probes into new media and Internet companies for possible anti-trust activities, targeting old-fashioned stationery manufacturers instead.