Irish fishing industry leaders dispute a claim by the European Commission that Ireland signed up to a deal which will wipe out the "tonnage" entitlements of many Irish skippers.
The complex issue is due to be decided by European Commission officials on July 15th, under Article 12 of the revised Common Fisheries Policy (CFP).
Mr Lorcan Ó Cinnéide, of the Irish Fish Producers' Organisation (IFPO), said that Commission officials were being "opportunistic" in claiming that they had the power to invoke such a decision.
The move could result in losses to Irish fishermen of up to €120 million, according to his organisation's estimates.
The issue is the latest shock to hit the fishing industry since the first challenge to the integrity of the Irish Box late last year.
The industry is also opposed to a "days at sea" regime, which currently ties up all whitefish vessels in the north-west for all but 11 days a month and which is to be extended by the Commission to the Irish Sea.
Now the EU Commission is claiming the right retrospectively to make null and void fishing entitlements held by Irish fishermen whose "tonnage" was not actually on the Irish fleet register on January 1st of this year.
Under a system administered with EU knowledge since 1990, fishermen seeking a licence for a new vessel must "retire" or "withdraw" equivalent capacity, known as "tonnage", equivalent to that being introduced.
Not only was the European Commission aware of the system, but it owes its origins to the EU - it was introduced as a response to EU limits on fleet size.
A recognised market in "tonnage" has developed as a result, and it is recognised as an asset or "property right" by the courts. It is also used to underpin bank loans to vessel owners.
As the IFPO points out, there are thousands of "tonnes" off the fishing register at any one time, as tonnage is in transit.
It has been accepted as "replacement capacity" or a form of guarantee towards licensing a new vessel.
"This proposal, if implemented, would mean that hundreds of small and large fishermen will be deprived of an asset which was theirs," Mr Ó Cinnéide said.