More than 300 business leaders in the UK are urging Britain to vote to leave the European Union, warning that the country's competitiveness is being undermined by its membership.
In a letter to The Daily Telegraph, they argue that businesses will be "free to grow faster, expand into new markets and create more jobs" if they are unconstrained by EU rules.
Signatories include Peter Goldstein, a founder of Superdrug; Steve Dowdle, a former vice-president Europe of Sony; David Sismey, a managing director of Goldman Sachs, and Sir Patrick Sheehy, the former chairman of British American Tobacco.
"Brussels's red tape stifles every one of Britain's 5.4 million businesses, even though only a small minority actually trade with the EU," they said.
"It is business - not government - which generates wealth for the Treasury and jobs for our communities."
The letter will be seen as an attempt by the Leave camp to counter a series of warnings by bodies such as the Bank of England and the International Monetary Fund that the UK will be worse off outside the EU.
Chancellor George Osborne will return to the offensive for the Remain campaign with a major speech warning of the economic dangers of Brexit.
On the Leave side, Boris Johnson will also be on the campaign trail with the Vote Leave battle bus after the controversy over his remarks comparing EU efforts to build a federal superstate to Hitler's attempts to dominate Europe.
Meanwhile, David Cameron has warned that leaving the EU would be a "national error" as part of an attempt to reach out to Labour supporters.
In an article for the Labour-supporting Daily Mirror, the British Prime Minister said he was backing Remain for the sake of jobs, security and Britain's place in the world.
"It's not every day you get a Tory Prime Minister writing in the Mirror. But then it's not every day we face a decision of this magnitude: whether to stay in the EU, or walk away," he said.
His intervention came amid concerns in the Remain camp that they are encountering significant hostility to the EU in traditional Labour areas.
On Saturday, Jeremy Corbyn appealed to supporters at a Labour In rally in London to blame the Conservatives, not Brussels, for the problems facing the country.
In his article, Mr Cameron emphasised he had been campaigning alongside Labour former foreign secretary David Miliband and ex-TUC general secretary Sir Brendan Barber, and praised Gordon Brown's "powerful and passionate" speech in support of Remain.
"I've been in this job for six years now. Whatever you think of me, I know how Britain gets things done in the world," he wrote.
"I've seen how free trade within Europe benefits working people. I've seen how manufacturing is boosted by trade deals the EU has done with the rest of the world. I've seen how shared intelligence keeps families safe.
"It's my deep, considered, steadfast belief that leaving Europe would be a national error, a big mistake."