Business needs to know what will happen on the day after Brexit as they consider a "cliff edge scenario" of a sudden transformation in trade, the Government is being told.
Paul Drechsler, president of the CBI, is to highlight areas of uncertainty such as access to Europe's markets and workers.
He will tell the business group's annual conference in London tomorrow (Monday) that companies wanted a "smooth" Brexit to avoid any "cliff edge" problems.
He will tell 1,000 businessmen and women: "Businesses are inevitably considering the cliff edge scenario - a sudden and overnight transformation in trading conditions.
"If this happens, firms could find themselves stranded in a regulatory no man's land and, even if our legal obligations are clear and in place, there would also be real, practical implications.
"Our ports, airports and logistics firms, if faced with new trading rules, could suddenly need new and potentially complex paperwork, which would take more time and money to process.
"As a result, they'd need more warehouses to store more goods on site and more supply roads for the vehicles waiting to deliver them. At short notice - this would be impossible."
Mr Drechsler will also warn that many people see business as run by a " privileged few", playing by a different set of rules.
"We need to acknowledge that there have been unacceptable transgressions, which have made people question the value of what we do and our right to do it," he will say.
"These cases are exceptions, but they're shaping people's view of all of us. On a range of issues we need to show not just that we're listening to people's concerns, but that we're acting on them.
"Firms should explain - in public - what steps they've taken on employee engagement and representation and we need to send out a strong message that rewarding failure is not an option.
"Exceptional pay can only be justified by exceptional performance. That's why we want the Government to introduce a binding vote on executive pay for 'repeat offenders' who fail, again and again, to satisfy shareholders with their pay decisions.
"We need to show people that business is on your side."
Mr Drechsler, who is chairman of social mobility charity Teach First, will add that business must remain "calm, confident and constructive" over Brexit.
A Government spokesman said: "We are determined to make sure that the UK remains the best place in Europe to run and grow a business.
"The UK will continue to be a global leader of free trade and we want to see British companies having the maximum freedom to trade with and operate in the single market.
"Our plans for a Great Repeal Bill, ending the authority of EU law by bringing it into UK law on exit day, will also ensure maximum certainty and stability for business."