Emerging evidence suggests European fishermen took part in unregulated and illegal tuna finishing in Libyan waters during the country's civil war earlier this year.
According to a report on the BBC's website, signals recorded from boat's electronic 'black boxes' show a significant presence inside Libyan waters, home to a major concentration of endangered bluefin tuna.
A letter from a former industry source is among several pieces of evidence that suggest EU boats may have been involved.
The European Commission has said any fishing in Libyan waters this year could be judged illegal.
EU Fisheries Commissioner Maria Damanaki told BBC News they are also investigating whether Italian authorities made bilateral deals with Libya on tuna-fishing. Such deals would contravene EU regulations.
The issue will be aired this week at the annual meeting of Iccat -- the International Commission for the Conservation of Atlantic Tunas – which opens in Istanbul on Friday.