Dairy farmers are facing a super levy bill of at least €15m for exceeding their production quotas last year.
It is thought that national production was 1% to 1.2% over quota in the year up to the end of March.
However, the Department of Agriculture, Food & the Marine said final figures will not be available for another two weeks.
Irish Co-operative Organisation Society spokesman George Kearns said a super levy of 28 cent will have to be paid to the EU for every litre over quota.
Farmers who exceeded their limits will get bills over the next few months.
Many of the country's 18,000 dairy farmers had exceptional difficulties staying within their quotas as they are now scaling up production before the EU abolishes quotas in 2015.
Milk output is expected to increase by 50% by 2020, which is a significant potential boost to exports.