One of Britain's biggest organisations will make the economic case for remaining in the European Union after a survey found eight in 10 firms backed the UK's continued membership.
But the Confederation of British Industry (CBI), which represents firms employing nearly seven million people, will not align itself with any EU referendum campaign group.
The group's final decision follows a survey of member organisations which indicated 80% of firms believed remaining in the EU would be best for their businesses, with just 5% saying it would be in their best interests to leave and 15% unsure.
The ComRes poll indicated that 71% of small and medium-sized firms believed that remaining part of the 28-member bloc would be in the best interests of their businesses, with 11% favouring a Brexit.
The survey formed part of a consultation process with the CBI's members and governing structures, leading to a final decision by the chairmen's committee - the organisation's highest policy-making body - to back making the case to remain in the EU.
But the CBI will not register with the Electoral Commission as a participant in the June 23 referendum contest.
The CBI's director-general Carolyn Fairbairn said: "The message from our members is resounding – most want the UK to stay in the EU because it is better for their business, jobs and prosperity.
"Walking away makes little economic sense and risks throwing away the many benefits we gain from being part of the EU.
"Our members tell us that having guaranteed access to a tariff-free market of 500 million people, and to more than 30 global trade deals covering 50 countries, are significant advantages that outweigh the frustrations.
"A minority of members want to leave the EU. We will continue to respect and reflect their views and campaign for EU reform to get a better deal for all businesses.
"However, most CBI members are unconvinced that alternatives to full membership would offer the same opportunities. We have yet to see those who seek to leave the EU present a compelling vision of what this would mean for jobs and growth.
"We will not align ourselves with any campaign. Though prosperity, jobs and future living standards matter to many people, we recognise there will be other considerations.
"It is not our place to tell people how to vote, but the CBI will play its role in making the economic case for remaining in the EU."
The survey of CBI members, which had 773 responses, found 77% believed that remaining in the EU would be in the best interests of the UK economy as a whole, with 6% saying Brexit would be better.
Some 85% of CBI members based in London said a Remain result would be in the best interest of their organisation, a figure that dropped to 75% in both the Midlands and East of England.
James Bardrick, chief executive of Citi Global Markets, part of the financial giant Citigroup, warned that "many firms" could think about moving jobs overseas if the country left the EU.
"Membership of the EU is one of the main reasons Citi's EMEA headquarters is in the UK," he said. "Being in the EU allows us to passport our financial services right across the single market, creating efficient access for our multinational clients operating throughout Union.
"Were the UK to leave the EU, many firms would probably have to rethink the way they do business, including whether to relocate certain activities."
Paul Kahn, the president of aerospace firm Airbus Group UK said: "If the UK exits the EU, there are likely to be significant changes to the regulatory and economic environment with subsequent impacts on our competitiveness.
"Though Airbus Group remains fully committed to its operations in the UK and to its employees here, we certainly hope the UK will choose to retain its EU membership which helps to ensure the continued long-term success of Airbus Group's European industrial model."
The CBI's decision follows controversy over the British Chambers of Commerce's former director-general speaking out in favour of Brexit.
John Longworth resigned after saying the UK could have a "brighter" future outside the EU, even though the BCC was staying neutral on the referendum issue.
Vote Leave chief executive Matthew Elliott said: 'It's welcome news that the CBI has seen sense and won't be seeking to campaign in the referendum.
"Dodgy polls from the CBI carry little weight after their long and regrettable history of getting it wrong on the EU."
He claimed the "EU-funded CBI" had acted as "little more than the Voice of Brussels". The CBI insists that funding it has received from Brussels is for "economic analysis" and it has no obligation to promote EU membership.
:: ComRes conducted a survey of 773 CBI member organisations online between February 22 and March 7. Results have been weighted to reflect the views of the CBI's member organisations as a whole.
Will Straw, executive director of Britain Stronger In Europe, said: "This demonstrates that there is significant support among Britain's small, medium and large businesses for remaining in Europe.
"Being part of the EU's free trade single market of 500 million people encourages investment, helps businesses to grow, creates jobs, and keeps prices low. Employers know that leaving would put all of this at risk.
"Leave campaigners now propose that Britain follows Canada's relationship with the EU, but this would mean paying more for less.
"New tariffs, for example on cars and beef, would push up prices. Britain would be left with no influence over EU regulations that we would be forced to follow.
"Worst of all, vital jobs in the services sector – such as fast-growing creative industries and financial services – would be at risk as they would no longer have access to the single market."