Unite, which has around 150,000 members in Scotland, has written to all 32 local authorities calling on them not to create a workplace parking levy (WPL) when they are given the power to do so.

The policy, which is designed to reduce congestion on the roads and cut air pollution, is being supported by the Scottish Government as part of a budget deal with the Greens.

Businesses in Scotland could be fined for failing to comply with parking levy

Staff could be charged for parking at work if councils bring in a new levy given the go ahead by the Scottish Government

Under the plans, ministers will support an amendment to the Transport Bill giving councils the power to introduce a parking tax for businesses and other employers.

If councils choose to do so, firms that provide free parking for employees will face new taxes, an extra cost they could then pass on to people who use the spaces.

The level of the fee will be set by individual councils, but a scheme operating in Nottingham charges £415 per space.

Unite’s Scottish secretary Pat Rafferty said council leaders should reject the new powers, which he claimed were being introduced without public consultation.

“The ability for councils to set a workplace levy through car parking spaces is a desperate attempt to absolve the Government from the funding crisis they have presided over,” he said.

“If implemented, we would have the ludicrous situation where we would have local authorities taxing workers for turning up to work.

“We believe that the Scottish Government should be facilitating public ownership of the nation’s buses and rail network, which would be a far better way to reduce car journeys through the provision of regular and affordable travel in Scotland.”

Unite’s intervention came as the leaders of all Scottish Conservative council groups signed a joint pledge against the parking tax, claiming it would “unfairly penalise workers”.

“If the workplace parking levy is introduced through legislation at the Scottish Parliament, Scottish Conservative councillors in my local authority region will oppose it,” the statement read.

“Instead, we will seek to provide better alternatives for our local region that support jobs and do not seek to punish staff for going to their work.”

The SNP said the Tory campaign against the tax was “embarrassing and hypocritical”, pointing out that the party’s councillors in Edinburgh backed a similar proposal last year.

During a meeting of the City of Edinburgh Council’s transport and environment committee in August, Tory councillors voted for an amendment which noted “the merits in principle of pursuing the power for Edinburgh to seek consent to introduce a Workplace Parking Levy”.

The amendment also called for the development of a paper on the possible pros and cons for the introduction of a WPL in the capital.

“Ultimately, it will be up to local authorities to decide whether a workplace parking levy is right for their areas,” SNP MSP George Adam said.

Union urges Scottish councils to rule out workplace parking tax