A workplace parking levy would help re-balance travel costs because driving is 10 per cent cheaper than 20 years ago, MSPs were told today.
Cycling and walking promoters Sustrans Scotland said the charge, which could be more than £400 a year per space, would also tackle congestion and pollution.
However, business and union leaders said many employers would pass the tax onto staff, some of whom had no alternative but to drive to work.
The groups were giving evidence to the Scottish Parliament's rural economy and connectivity committee over the proposal, which has been added to the Scottish Government's transport bill as part of a Budget deal with the Greens.
It would give councils the power to charge companies and other employers for parking spaces on their premises.
The money raised would be ring-fenced for improving public transport.
Sustrans Scotland senior policy officer Alex Quayle said: "Since 1997, the cost of motoring is down 10 per cent in real terms.
"Bus fares are up 7 per cent, rail fares up 5 per cent.
"The least desirable forms of transport are being prioritised in a flat way, regardless of your capacity to afford them or not.
Mr Quayle said the levy would be a "relatively small financial mechanism that can re-balance that."
He said motoring costs also did not take account of the impact of vehicles on congestion and pollution.
He said workers on the lowest incomes were likely to benefit from the levy because they were less likely to own a car and more likely to live in areas suffering air pollution and higher road casualty rates.
Sue Flack, a policy adviser for sustainable transport campaigners Transform Scotland, said: "Continuing to make motoring cheaper will only encourage more people to drive."
Stuart Douglas, Smarter Choices Smarter Places manager for developers Paths for All, told the committee: "We have a climate emergency.
"Transport is the biggest cause of emissions and 60 per cent are from cars.
"We cannot accept the status quo."
Earlier, insurer Aviva told the committee it backed a levy because the measure would reduce the number of cars on the road.
However, Fiona Beale, its head of corporate real estate, said the firm should potentially be exempt because of the work it did to promote other forms of transport.
These included funding bus improvements, car-sharing and cycling.
Helen Martin, assistant general secretary of the Scottish Trades Union Congress; said the levy would potentially fall heavily on low-paid workers, such as shift workers.
She questioned whether it would raise enough money to make much improvement to public transport.
Ms Martin also feared councils would just use the revenue to replace current transport spending.