The Scottish Government is facing growing pressure to spell out how a controversial new charging regime for Scots to park at work will operate.
It has emerged that senior SNP figures, including Deputy First Minister John Swinney, have previously opposed such a proposal.
The Tories now say the scheme could "fall apart" before it has even begun.
The workplace parking levy was among a suite of new taxes unveiled last week as a part of a budget deal with the Scottish Greens. But its has prompted a backlash among business leaders and motoring organisations with concerns that commuters could now be charged as much as £500 a year to park at work.
NHS staff will be exempt, but it remains unclear if teachers will be excluded or whether it applies to blue-badge holders and emergency service workers. There is also no indication if small businesses will be supported.,
There are also concerns about the impact on rural areas where people often have no choice but to drive to work.
Read more: Parking levy in Scotland ‘could force teachers to quit the profession’
Tory finance spokesman Murdo Fraser said if ministers can’t offer urgent clarification on the levy, they should drop it altogether.
“It’s blatantly obvious this knee-jerk experiment has been dreamed up in a hurry, and there’s basically no detail at all," he said.
“If the SNP government doesn’t start answering these questions, the whole tax could fall apart before it’s even begun.
“It’s becoming increasingly clear that the SNP had to throw a bone to the Greens for budget support, and this ridiculous proposal was it.
“Senior figures in the party are even on record opposing it.
“This is an unpopular idea, and one which will hit the finances of businesses and their hardworking staff.
“Instead of lumping more levies on businesses, the SNP government should be finding ways to help them thrive.”
It has also emerged that the SNP has repeatedly opposed similar plans.
In 2000, Mr Crawford said: “We were never convinced that workplace charging was the way forward.”
In the same year, Mr Ewing stated charges were “not appropriate” for rural Scotland.
And former finance secretary John Swinney warned that some people would park in nearby residential areas to avoid the levy.
Since the announcement in Holyrood, the proposal has been widely criticised by businesses and motoring groups.
But a Scottish Government spokesperson said: “Plans to give powers to councils to introduce a Workplace Parking Levy, as already allowed in England, will come forward via an agreed Green Party amendment to the Transport (Scotland) Bill. We have said that this is contingent on exemptions for health service workers and will be engaging with stakeholders in the run-up to Stage 2 of the Bill to help shape the specifics on the Workplace Parking Levy for the amendment to the Bill.”