Community and business leaders with Commonwealth links have written to David Cameron to urge him to back Britain's exit from the EU.
The 80 signatories include leading figures in the Asian hospitality industry and award-winning gospel singer Rachel Kerr.
The PM is expected to recommend Britain remains in a reformed EU.
Remain campaigners said several Commonwealth leaders, including India's PM, had urged Britain to stay in.
The 80 figures from Britain's Commonwealth community criticised Mr Cameron for a lack of ambition in his EU reform demands, which he hopes to put to the public in a referendum in June.
They claimed the UK government's immigration policy discriminates against non-EU citizens.
In their letter to Mr Cameron, published by the Vote Leave campaign, they say: "As patriotic Britons of Commonwealth backgrounds, we saw the EU renegotiation as an opportunity to rediscover Britain's global vocation.
"As long as Britain's trade policy is controlled by the EU, we cannot sign bilateral free trade agreements with Pakistan, India, Bangladesh, Australia, New Zealand or for that matter any other non-EU state.
"Vested interests on the Continent sustain a relatively protectionist policy. We have to apply the EU's common external tariff to exports from Commonwealth countries - hurting consumers here as well as producers there.
"At the same time, our immigration policy forces us, in effect, to turn away qualified workers from the Commonwealth so as to free up unlimited space for migrants from the EU.
"The descendants of the men who volunteered to fight for Britain in two world wars must stand aside in favour of people with no connection to the United Kingdom."
One of the signatories, Pasha Khandaker, president of the UK Bangladesh Caterers Association UK, said the 12,000 curry houses his organisation represents "have been struggling to recruit the talent that they need because of the difficulties associated with employing people from outside of the EU".
"If the UK had a fairer immigration system it would be easier for businesses to recruit skilled workers regardless of their nationality," he added.
Other signatories include Rachel Kerr, who won a Mobo award in 2012, in the gospel music category, and Moni Verma, founder of Veetee Rice, a UK-based food business with a turnover of £80m a year.
A spokesman for Britain Stronger in Europe said: "Several Commonwealth leaders have been very clear that Britain is stronger, safer and better off in Europe.
"Indian Prime Minister Narendra Modi said Britain is the entry point for trade right across Europe; while Australia's former deputy prime minister said the Commonwealth could never replace the trade Britain does with the EU.
"We get the best of both worlds in Europe, trading freely with the world's largest market, as well as accessing free trade deals with over 50 countries around the globe.
"While Leave campaigners may look back with rose-tinted spectacles, they have no plan for what Britain outside the EU would look like, and no guarantee that trade, jobs and prices wouldn't be hit."
In a separate development, 63% of business people polled by the British Chambers of Commerce said David Cameron's EU negotiations would not change the way they will vote in the referendum.
The internet survey of 2,133 BCC members found 60% would vote to remain, down slightly from 63% in a previous poll in September, with 30% saying they would vote to leave, a 3% increase.
Those representing large firms were significantly more likely to vote 'remain' than small-business people.
BCC director general John Longworth said: "Our findings suggest that for business people, this is a question of in or out - not renegotiation."