Anti-Nice Treay campaigners are being "dishonest" in their claims, according to the Chambers of Commerce of Ireland (CCI).
In starting its campaign for a Yes vote, chief executive Mr John Dunne cited this alleged dishonesty as the main reason why the CCI were "obliged to produce briefing materials for our members to counter their constantly repeated lies".
Mr Dunne also dismissed claims made by No campaigners that Ireland would lose its commissioner as "blatant untruths" and condemned what he called "fascist tactics".
"We're calling on them to end their campaign of dishonesty and start dealing with the facts," he added. Mr Dunne rejected claims by the No campaign that the Nice Treaty was unnecessary and that enlargement would be possible without the yreaty being passed by all member states.
As it stands, under the Amsterdam Treaty only five additional countries can join the EU, he claimed. "But no fewer than 12 countries are negotiating for entry and the Nice Treaty is necessary for those countries to join".
This enlargement, he said is a "critical factor" in investment decisions into Ireland.