84% of chief executives believe the rejection of the Lisbon Treaty damaged Ireland’s international reputation, according to a new survey by the Irish Business and Employers’ Confederation.
The study of 300 chief executives also found that 98% felt that EU membership has been important to the success of Irish business.
IBEC has said a Yes vote in the referendum in October is an essential step on the road to economic recovery.
The employers' group said it will send a positive signal to Ireland's European and international partners.
In Dublin, a new campaign for a Yes vote has been launched. Olivia Buckley, the director of the 'We Belong' group, promised a straight-talking campaign in the ten weeks running up to polling day.
Former Republic of Ireland goalkeeper Packie Bonner and businessman Bill Cullen are among the campaign's high profile supporters.
Mr Bonner said he had been confused about the issues in the first referendum but that a lot of those doubts had now been cleared up.
Mr Cullen said it was time to say Yes to Lisbon and Yes to Ireland being in Europe.
The second referendum on the treaty will be held on 2 October.