Remaining in the EU will benefit workers, businesses and the community and voluntary sectors, campaigners have claimed.
A consortium including CBI director Nigel Smyth, Glyn Roberts of the Northern Ireland Independent Retail Trade Association, and Manufacturing NI, said that "in representing businesses, workers and the voluntary and community sector, we are firmly of the view that Northern Ireland's future prosperity is better off within the EU".
The message was also endorsed by Peter Bunting, general secretary of the Irish Congress of Trade Unions, Northern Ireland Council for Voluntary Action chief executive Seamus McAleavey, Northern Ireland Food and Drink Association director Michael Bell and Londonderry Chamber of Commerce chief Sinead McLaughlin.
"We are clear that continued membership of the European Union will benefit local workers, employers, consumers and our community and voluntary sector," the group of different organisations said.
But DUP councillor Lee Reynolds, who is heading up the Leave campaign in Northern Ireland, rejected the claims.
"When voters look at the ballot paper, they will not see the word reform on it - that is because a reformed EU is not on offer," he said.