The employers' group IBEC plans to spend €500,000 promoting a Yes vote on the Nice Treaty.
A campaign on this scale is unprecedented for the group, which has already raised over €250,000 from its members.
The IBEC director-general, Mr Turlough O'Sullivan, said that a poster and billboard campaign would begin in about a week's time. Explanatory booklets about the treaty had been sent to all 7,000 IBEC member-organisations, who were being encouraged to discuss the issue with their employees.
"We watched in amazement last year as anonymous and undeclared forces blitzed our streets with claims which a reading of the treaty would show to be very misleading," Mr O'Sullivan told a news conference at IBEC headquarters in Dublin yesterday.
He continued: "It is important that the public know where everyone in the campaign is coming from and how their campaigns are funded. As I said, we still do not know what forces funded the omnipresent 'No' posters that we saw last year or what really motivated the invisible organisations that funded that campaign.
"Our information programme will be up-front in every sense. You will know why Irish business is calling for a 'Yes' vote. You will know how it has raised money for our information programme, and you will know how it spends that money.
"The IBEC president wrote to members before the summer. The largest businesses were asked for a contribution of €5,000, middle-sized businesses for €2,000, €1,000, and a sliding scale down to small businesses that were asked for contributions of €100."
Describing anti-Nice campaigners as "Little Irelanders" who offered only the "isolation that strangled Ireland" in the past, Mr O'Sullivan said that IBEC would still be around when the ballot-boxes closed.
"We cannot creep up in the night to put up posters and then run before we have to answer questions," he added.
The IBEC president, Mr Maurice Pratt, said that a larger European market would promote employment. "I am not aware of any leading figure on the 'No' side of this campaign who has ever created a single job."
Mr Pratt, who is chief executive of the Cantrell & Cochrane drinks group, said: "A Yes vote is a vote to give us influence and prosperity in a larger Europe. A No vote is a vote towards isolation."
The director of the IBEC campaign, Ms Maria Cronin, said that funds had been raised on a voluntary basis from members, but it would not be appropriate to list individual firms.
Guest speakers at an IBEC conference on Nice next Friday will include the European Commissioner, Mr David Byrne, and the President of the European Parliament, Mr Pat Cox.
Meanwhile, the youth group Ireland for Europe has sent an open letter to the Taoiseach urging him to hold the referendum on a Friday to give young people who are working away from home an opportunity to vote when they return for the weekend.
The Minister of State for European Affairs, Mr Dick Roche, has accused anti-Nice campaigners of displaying "extraordinary arrogance" on the economic consequences of a No vote. "They are willing to take risks, big risks, with peoples' jobs and wellbeing. They are playing with fire. That is politically irresponsible," he said in a statement.
Mr John Cushnahan, Fine Gael MEP for Munster, has interrupted his work as chief EU election observer of the Pakistan general election to spend two weeks canvassing for Nice. He will return to Pakistan a fortnight before the election, which takes place on October 10th.