The Irish Fishermen’s Organisation (IFO) said a No vote would tell Europe the deal it had worked out should be scrapped.
Caitlín Uí hAodha, spokeswoman for the IFO, said those unsure about the treaty can use their ballot to assist the plight of fishing communities.
“If you don’t know vote No, because we need your support,” she said.
Ms Uí hAodha said the common fisheries policy was a deal which favoured the larger countries to the detriment of Ireland’s fishing industry.
She said Europe had to be told the manner in which it dealt with Ireland was unacceptable.
Chairman of the IFO, Ebbie Sheehan, said aspects of the indigenous fishing industry were being criminalised by European regulations but these were not being applied in other member states.
The IFO representatives were speaking at a combined press conference of anti-Lisbon campaigners.
Farmers for No spokesman Councillor Billy Clancy also spoke.
He said farmers could no longer afford the policy direction taken by Europe.
Mr Clancy said when Ireland joined the union a 50-acre farm would generate an income equivalent to the average industrial wage but now a farmer needs to be working an excess of 200 acres.
He said environmental regulations had hamstrung farmers’ ability to earn a living and were excessive and unnecessary, he said.
People’s Movement leader Patricia McKenna, a former Green Party MEP, said Ireland would lose a huge portion of its strength around the union’s negotiating table.
“How can we be stronger in Europe with less voting strength? It just doesn’t make sense,” she said.
She asked people to vote on the treaty which was rejected last year and not the guarantees which would not be included at a later date. The guarantees would not have the same legal authority as the treaty itself, she said.
Artist Robert Ballagh chaired the press conference and said a Yes vote would have far greater implications than people appreciated. He said hypothetically the GAA could be forced to change its amateur status if the Lisbon Treaty is passed.