Hundreds of staff at the National Trust for Scotland are being asked to consider strike action as part of a row over pay, union leaders said.

The Prospect union, which represents almost 350 employees at the conservation charity, said it was balloting members on industrial action over a pay settlement imposed by bosses.

The union wants to see the living wage of £7.45 an hour introduced for all staff, saying some workers at the National Trust for Scotland (NTS) earn £6.42 an hour.

But it said the NTS was instead upping pay to £6.67 for its lowest-paid workers, with the promise of achieving the living wage by 2017.

Prospect said 91% of its members had already rejected the pay offer - which it claimed amounted to a 2% pay cut in real terms.

The union further claimed staff had seen the value of their pay reduced by almost a quarter since new grades were introduced in 2005.

Prospect national secretary Alan Denney said: "Members have made it clear that enough is enough.

"They accept that a price had to be paid to secure the trust's future and they are not seeking to recover these losses in pay. They want to see their pay keep up with prices.

"Significant numbers of staff are paid at minimum wage levels and they deserve better than another pay cut."

The NTS was established in 1931 to protect and promote Scotland's natural and cultural heritage for present and future generations to enjoy.

NTS director of HR George Wilson said it was "very sympathetic to the demands being made by Prospect ", adding: "We too wish to improve the rewards we give to our staff.

"However as a charity which depends on membership fees and donations for survival and is fighting its way back from the financial brink, we can only pay what we can afford.

"Over the last three years we have invested in staff pay and conditions equivalent to a 15% increase. We now have no staff whatsoever either on or earning less than the national minimum wage.

"This year we have implemented a pay deal which is the fairest we can manage and represents an overall 2% investment, with the lowest-paid staff receiving the greatest share.

"We have also agreed to longer-term commitments in relation to pay progression and working towards full implementation the Scottish living wage over four annual instalments.

"Compared to what many in the public and private sectors are enduring in the current climate, we think this is a pretty good deal."

Mr Wilson added: "Prospect chose not to ballot members on our final, enhanced pay offer and rejected it out of hand, despite it providing most of what Prospect were asking for - but over a timeframe and conditions of affordability that are realistic given our current financial situation.

"Prospect have not budged from the position of wanting an 8% increase leading to a massive rise in our pay bill that we simply can't afford."