Staff at Quarriers went on strike yesterday in a dispute over pay in what is believed to be the first industrial action in the 137-year-old history of one of Scotland's biggest charities.

About 100 Unison members took part in a one-day walkout at four of 127 projects run by Quarriers across Scotland and in Bath.

The dispute is over an offer of 2.5% and a refusal by management to target rises at the lowest-paid staff members.

Projects affected included Seafield School in Ardrossan, North Ayrshire, which caters for 66 boarding and day pupils with social and emotional behavioural difficulties, and North Ayrshire Supported Living in Saltcoats, which provides shelter for young men and women aged 16-25.

Unison members at the Stopover and James Shields homeless projects in the south side of Glasgow, which also provide shelter for young men and women, also went on strike. Quarriers said the action had little impact but Unison said it was "very successful" and warned of more to come unless Quarriers improved its pay offer.

Quarriers says it is concerned, in common with other voluntary sector organisations, that overall local authority contracts income falls short of what it needs to pay staff the increase they have demanded.

The charity's chief executive, Phil Robinson, said project residents used their services as normal yesterday. Quarriers staff completed risk assessments and took appropriate measures to minimise risk to people being supported at the projects.

He added: "We are happy to meet Unison again to discuss the pay issue, but we are not able to improve our pay offer."

The union has expressed sympathy with Quarriers' case but has argued that the Scottish Executive and local authorities should pay for the services provided by Quarriers and other voluntary sector organisations on the basis of full cost recovery''.

Simon Macfarlane, Unison's regional officer in Scotland, said: "Other voluntary sector organisations have been able to settle wage demands by staff. This hasn't happened in the case of Quarriers which has a responsibility as an employer to pay decent wages to the staff who carry out such work.

"We will look at taking more widespread action unless management make an offer which is acceptable to staff."