Campaigners battling to block the A9 average-speed cameras scheme claim the project will cost the Highlands 20,000 working hours every day.
And they fear increased journey times on the key trunk route could lead to major employers opting to relocate staff further south.
The head of the A9 Average Speed Cameras Are Not The Answer group spoke out after an Inverness businesswoman said an hour had been added to the trip to her firm’s Edinburgh offices.
Transport Scotland has just released figures showing drivers were slowing down as a result of the cameras being installed on the route – despite the fact the devices have not even been switched on yet.
The statistics have heightened fears that the Highlands’ vital tourist industry and wider economy will be badly affected.
Nathalie Agnew, director of public relations firm Muckle Media, said she was losing two hours on her regular journeys between her Inverness and Edinburgh offices.
She said: “That is time I could be working. Running a small business, your time is really precious.
“My concern is that even before the cameras have been switched on drivers are changing their behaviour. When the cameras are switched on, it will just get worse.”
Foyers-based campaigner Mike Burns said Miss Agnew’s experience backed up what drivers were reporting to the pressure group.
He said that with at least 20,000 journeys a day on the road, the same number of working hours were being lost.
He likened it to 2,500 jobs disappearing on a daily basis.
“Increased journey times are already putting tourist off coming up to the Highlands,” said Mr Burns.
“You have staff who have to plan extra time travelling, therefore they are spending more time stuck in their cars and are not being productive.
“Are companies going to start relocating staff because of this? Are we going to look at a potential drain from the Highlands?”
Inverness Chamber of Commerce chief executive, Stewart Nicol, said the organisation’s concern had always been the impact on businesses who want to get to the central belt.
He said there was no credible alternative route to the Highlands and the main railway line was at capacity, which meant passengers heading north could not get to Inverness before 10:30am and those going the other direction to Glasgow before 10:15am.
He said: “We can get to the centre of London with the airlines quicker than we can get to the centre of Edinburgh. It just makes doing business so much more difficult.
“There is a concern around the average-speed cameras that they will impact on business.
“None of us want to see another accident on the A9. We all want to see the route dualled.”
Transport Scotland said traffic counters installed on the A9 between Perth and Pitlochry showed that one in three vehicles exceeded the speed limit before the installation of the cameras.
Counters were then installed on two separate dates earlier this month at different locations where there are speed cameras.
Both showed 8% of vehicles speeding.