Reports as far back as November have emerged that farmers have been trying to smuggle their over-quota produce into the Northern Ireland market.
The Department of Agriculture has written to all milk purchasers in the State to warn of this illegal activity.
The ICMSA has said individuals caught selling black milk to unregistered buyers faced “savage fines” and warned that individuals could not be allowed go “outside” the system.
It estimates that Ireland is currently running around two per cent over its national quota, which may mean a fine of €31m.
Meanwhile the Irish Farmers Association (IFA), the Ulster Farmers Union (UFU) and Dairy UK have also raised concerns of cross-border selling of milk to unregistered purchasers.
The IFA has called on farmers approached with such offers to report them to their co-op and the Department of Agriculture.
Speaking to AgriLand previously UFU President Harry Sinclair said: “This is a very serious issue that threatens the integrity of our entire dairy industry. It appears that a few unscrupulous individuals are potentially putting the good reputation of farmers at risk. I would strongly discourage anyone from getting involved in these illegal activities and would go further and ask everyone to be vigilant and to alert the authorities immediately of any suspicious activity happening in your area.”