British Prime Minister David Cameron heads to Scotland Thursday to make the business case for it remaining part of Britain as 200 business leaders signed an open letter backing independence.
Questions over whether Scotland's economy could go it alone have been at the heart of the campaign, with a rival group of 130 captains of industry claiming Wednesday that independence would be "bad for business".
Scotland votes in three weeks' time on whether to become a separate country after over 300 years of union with the rest of the United Kingdom.
Most opinion polls currently suggest the proposal is set to be rejected.
The "Yes" and "No" camps have traded statistics and accusations on everything from whether Scotland could keep using the pound to what share of Britain's national debt it should take on if it broke away.
Cameron kept a low profile on the campaign trail due to his centre-right Conservative Party's unpopularity north of the border, where it only holds one out of 59 House of Commons seats.
But he will re-enter the fray by urging Scots not to turn their backs on "one of the oldest and most successful single markets in the world" in a keynote speech to CBI Scotland, a leading business lobby group, in Glasgow.
Cameron is set to say that Scotland does twice as much trade with the rest of the United Kingdom as with the rest of the world put together, according to pre-released extracts of his speech.
He is also expected to highlight "the opportunities that come from being part of something bigger".
As the prime minister was set to arrive in Glasgow, The Herald newspaper published a letter from 200 business people arguing that an independent Scotland would be better for business.
This is because policy would be set by people "who truly understand and care most" about Scotland, not politicians in London, according to the letter.
It added that independence would provide "more opportunities for our talented and determined young people to stay and succeed".
The signatories range from big business leaders such as Brian Souter -- chairman of major transport group Stagecoach and a prominent donor to the independence campaign -- to the owners of smaller enterprises such as guest house owners.
The letter comes the day after over 130 captains of industry signed another open letter in The Scotsman newspaper saying "the business case for independence has not been made".
Many of the signatories to Wednesday's pro-union letter worked for big name international firms.
They included Andrew Mackenzie, chief executive of mining giant BHP Billiton, Douglas Flint, group chairman of HSBC bank and Simon Thomson, chief executive of oil and gas exploration firm Cairn Energy.
The pro-independence letter featured more bosses from small and medium-sized enterprises who said they employed a combined total of 50,000 people, but stressed they did not speak for their employees.
First Minister Alex Salmond, who is leading the "Yes" to independence campaign, argues that the British government's economic policies are unfairly skewed in favour of London and southeast England.
He said business leaders were "waking up to the opportunities of independence".
"With full control over economic powers, we have the opportunity to tailor economic policy to our needs," Salmond added.