The British government could face heavy fines from Brussels if it fails to prove it is cracking down on illegal dumping in Northern Ireland.
It is estimated there are dozens of illegal dumps across Northern Ireland containing rotting industrial and household waste from both sides of the Border.
Criminal gangs have also been profiting from running illegal dumps, many of them bringing waste from the Republic.
European Commission officials have given the British government two months to respond to concerns that it has failed to prevent some dumps handling waste that could harm human health and the environment.
They have also told Department of Environment, Food and Rural Affairs officials in London they believe the government has also failed to prevent a number of sites acting in contravention of their waste disposal licences or operating without any licence at all.
The warning came after environmental campaigners alerted the commission to a number of dumps which are believed to be operating illegally in the North.
If the commission is unhappy with the government's response, its concerns could be referred to the European Court of Justice where Britain could face hefty fines.