The founder of Barrhead Travel has told his staff that a "Yes" vote in Scotland's independence referendum would be "a disaster".
Bill Munro sent a memo to staff about what he saw as the dangers of independence and accused the SNP of misleading voters.
Business for Scotland, a pro-independence group, said Mr Munro's arguments "didn't make sense".
The businessman said he had the right to express a personal opinion.
Barrhead Travel is one of the largest independent travel agencies in the UK, employing 800 staff in more than 50 branches.
The memo from Mr Munro was sent to all staff and directors of the company, and was subsequently leaked on social media.
Mr Munro's message said: "I have been asked by many of my staff what my views of the referendum are."
The memo went on to say that independence would be "a disaster", particularly for Barrhead's branches in England and Ireland.
It said: "As the weeks pass and more is discovered, the magnitude of the impending disaster should there be a 'Yes' vote becomes ever more apparent."
Mr Munro attached a copy of the Lyddon report, which was critical of the business implications of Scottish independence.
Gordon MacIntyre Kemp, the chief executive of pro-independence business group, Business For Scotland, said Mr Munro's arguments "don't make any sense".
He said: "Business for Scotland believes the business case is clear.
"The idea that in the event of a Yes vote, for example, there would be restrictions on trade, as outlined in the memo, doesn't make any sense. Day in, day out there is free trading taking place between independent countries.
He added: "Business for Scotland would be happy to outline the overwhelming case for independence to Bill Munro and let him see why we believe it is the business opportunity of a lifetime."
Mr Munro has also been criticised by "Yes" supporters on Barrhead's Facebook and Twitter pages.
'Put at risk'
In response to the criticism, Mr Munro said: "I decided to share my personal opinion which is that independence would not be good for Scotland, its businesses or its consumers.
"The opinions expressed are my own and not those of the company. Just as I have the right to express my own opinion, I respect that is true of everyone in Scotland, including the 800 employees of Barrhead Travel who will make their own views clear throughout the democratic process."
MP Jim Murphy, who was speaking on behalf of the pro-Union Better Together campaign, said Barrhead Travel was "yet another example" of an employer in Scotland saying that being part of the UK "is better for their business".
He added: "Being part of the UK means we can have the best of both worlds - a strong Scottish Parliament, with the guarantee of more powers, backed up by the strength, security and stability of being part of the larger UK. Independence puts that at risk."