Three out of four schools in Scotland face strike closure
Three out of four primary and secondary schools in Scotland face being closed during three days of strikes by non-teaching staff later this month.
The Unison union said 21,000 of its members working across 24 local authorities will walk out from Tuesday 26 to Thursday 28 September.
They will be joined by Unite members in 11 council areas.
The GMB, which had called off strikes for next week, also confirmed it would join "the concerted industrial action".
Those going on strike include cleaners, caterers, janitors and school support assistants.
The unions have rejected an average pay increase of 5.5% - with a 99p-an-hour rise in the living wage for the lowest paid.
Unison said its members remained "steadfast in their resolve to fight for fair pay".
Unison spokesman Mark Ferguson said: "Cosla's offer falls short of Unison's pay claim, it is also less than the offer made to the lowest-paid local government staff south of the border.
"No-one wants to see schools close but Cosla need to come back with a significantly improved pay offer very soon if strike action is to be avoided.
"We remain committed to engaging in negotiations with Cosla and the Scottish government at any point to try to resolve this dispute."
Rejected offer
Unite general secretary Sharon Graham added: "The entire blame for this situation is down to Cosla's ineptitude, and the Scottish government's dithering.
"Unite's hard-working council members deserve far more than 5%. They will have their union's total support in the fight for better jobs, pay and conditions in local government."
GMB Scotland's Keir Greenaway said the strikes were not yet inevitable but Cosla "was running out of time to avert industrial action".
He added: "We have tried repeatedly to find a way forward with Cosla but until an improved offer is made, one that workers believe is acceptable, then disruptive action seems increasingly inevitable."
It is understood council leaders have agreed to make an extra £10m available to fund an improved pay offer in a bid to avert strikes by GMB, Unison and Unite within weeks.
However, any improved pay offer, which must be agreed by all 32 councils, is likely to be well short of what the unions would ideally want.
The Scottish government has told Cosla it will not provide any more money to fund a pay deal.
The industrial dispute involves staff including catering, cleaning, pupil support, administration and janitorial workers in schools and early years centres.
Cosla previously said the "strong offer" raised the local government living wage by 99p to £11.84 per hour.
The council unions hope the threat of a three-day strike will focus the minds of council leaders and bring about what they would regard as an acceptable pay offer.
The strike would cause massive disruption in schools across much of the country. If janitors are on strike, schools may not be able to open.
But is a big enough improvement in the pay offer possible?
Council leaders agreed earlier this week to put an extra £10m into the pay pot across Scotland.
The Scottish government has told council body Cosla it cannot provide any more money just now specifically to improve the pay offer.
The new pay offer is expected to be made next week. As things stand, the new offer is likely to fall well below the aspirations of the unions.
The question is whether the new offer may be seen by union members as the best which can realistically be made at present - or whether it is rejected, adding to the likelihood of the strikes going ahead.