Staff in some of Scotland's biggest hospitals are to be balloted on strike action in the ongoing row over car park charges.

Unison plans to ballot members employed by NHS Greater Glasgow and Clyde who have to pay for taking their car to work.

The health board began introducing the controversial parking charges for patients, staff and visitors in 2005.

A recent review saw cuts in charges at many hospital sites but Unison said nurses and other workers remained angry about the policy, which it describes as a "tax" on staff for doing their jobs.

The union claims that full-time theatre nurses are having to pay up to £140 a month in parking charges.

And nightshift workers are being handed tickets when they finish work at 8am as the charges come into force a half-hour before.

Regional organiser Matt McLaughlin said: "Our members are very angry over these charges, and they are even angrier that their employer has refused to listen and has pressed on with these proposals to tax staff for coming to their work.

"It is unacceptable that vital health care staff have to pay up to £140 per month for parking and I believe that they are prepared to take action to make their employer listen."

As well as Greater Glasgow, a further four of Scotland's 14 NHS boards currently charge for car parking, including Lothian and Grampian.

The charges have been introduced to avoid non-hospital users taking advantage of the free parking.

Other factors cited by Greater Glasgow include the need to upgrade existing car parks and eliminate traffic congestion in and around hospital sites.

The charges were the focus of a discussion in the Scottish Parliament earlier this year.

In February the then First Minister Jack McConnell told hospitals to reconsider their charging arrangements after he was taken to task by angry nurses at a public meeting in Glasgow.

New arrangements have since been introduced at Glasgow hospitals, cutting the maximum daily parking charge from £12 to £7.

The number of patients and visitors qualifying for free parking was widened and a new sliding scale for staff permits was created, reducing the monthly charge to £5 for the lowest earners.

A poll published last month found that more than eight out of ten people believe that hospital parking charges should be scrapped altogether however.

The YouGov study for the Royal College of Nursing (RCN) Scotland showed that 87% of those surveyed supported the abolition of car parking charges for patients, visitors and staff at all NHS premises.

Mr McLaughlin said he remained hopeful that a dispute could be avoided and urged NHS bosses to meet with union officials.

He said: "I've written to the employers today, asking them to suspend this scheme and to meet with Unison in an attempt to reach a conclusion that helps them manage problem parking on specific sites, but does not tax staff, patients and visitors in the process.

"If they are prepared to meet with us and listen, I'm sure our members will see that as a step in the right direction."