Scottish independence would prove costly to companies on both sides of the border, according to a business lobbying group.
The CBI is "not convinced of the business and economic case" for independence.
During a speech in Glasgow, CBI director-general John Cridland will voice his concerns about Scotland leaving the UK.
He will stress the positive things that Scotland and England do together, such as Team GB's success at the Olympics.
Addressing the CBI Scotland annual dinner, Mr Cridland will say: "The CBI has a collective view on independence and, I believe, a duty to express it. CBI Scotland council is not convinced of the business and economic case for Scotland seceding from the Union and judges that businesses - Scottish, English, British - would lose out from the fragmentation of our single market.
"We have two years to get this right, and get it right we must."
If people in Scotland vote to leave the UK, the CBI would "work with the mandate". But a Yes vote would bring "several more years of upheaval and negotiation", he will argue.
"The immediate effects would be profound and, in the short term, costly. When Slovakia separated from the Czech Republic, it cost the country 4% of its GDP in the following year."
Uncertainty is the "biggest bogeyman of all" for business and the debate over Scotland's future is "adding a thick layer of uncertainty", he will say.
"What's on offer here is often described as divorce. Those proposing a permanent split say there's no animosity in this. It's just that after 300 years of relatively happy marriage, they feel it's time we started seeing other people. My view is: that's the wrong way to look at it."