Belgian authorities took around a month to notify European authorities about the discovery of eggs contaminated with an insecticide, t he EU's executive arm has said .
Dozens of poultry farms in Belgium and the Netherlands have been investigated amid the hunt for eggs containing Fipronil, which is dangerous to human health.
Millions of eggs have been pulled from stores in Belgium, the Netherlands and Germany, while Britain, France, Sweden and Switzerland have been warned that contaminated eggs might be on their territories.
European Commission spokeswoman Mina Andreeva said "no information about this contamination incident was provided" until July 20. Tainted eggs were found in Belgium in June.
She said EU states "have a legal obligation" to notify the commission immediately if they have information about a threat to human health.
Ms Andreeva declined to say more given that a legal probe is under way in Belgium and the Netherlands to establish who knew what and when.
Belgian food safety authorities say that of 86 farms checked, 21 were found to have traces of Fipronil, which is banned in products for animals like chickens that are part of the human food chain.
The levels detected are seven times below the European limit for what is considered dangerous.
It is believed that Fipronil got into the food chain when it was illegally added to a product used to treat poultry for lice and ticks.
Belgian agriculture minister Denis Ducarme has vowed to shed light on the contamination, but said consumers are not at risk.
"There is no danger today to public health," he told state broadcaster RTBF. "It's important that consumers understand this, all the eggs that could have been contaminated have been blocked" from reaching shop shelves.
He underlined that the Fipronil levels found are "well below the European limit". No egg shortages have been signalled at Belgian supermarkets.
In the Netherlands, Marieke van der Molen of the National Public Prosecutor's office for serious fraud, environmental crime and asset confiscation said the office is investigating the company suspected of using Fipronil and its supplier. She declined to name either company.
She said investigators have seized samples and administrative paperwork in the probe and are working closely with Belgian authorities.