The leaders of some of Britain's biggest companies have signed a letter saying leaving the EU would put the UK economy at risk and threaten jobs.
The letter, published in the Times newspaper, has signatures from the bosses of Marks & Spencer, Vodafone and BT.
British Prime Minister David Cameron has called an in-out referendum on EU membership for June, after securing a package of reforms in Brussels.
However, those supporting the OUT campaign say leaving the EU would cut costs and regulation for business.
And as UK political correspondent Theo Usherwood reports - the business community is by no means united.
IN: "It is…
OUT: …or leave."
DUR: 26 seconds
ALT:
Simon Walker of the Institute of Directors says big business was always likely to back staying in the EU.
IN: "I don't…
OUT: …of Europe."
DUR: 24 seconds
ALT:
Rory Broomfield of the Better Off Out campaign says the threat to Britain's trading arrangements with Europe is being exaggerate.
IN: "To say…
OUT: …the world."
DUR: 28 seconds