Councils and the Scottish government have not learned lessons from last year’s local government strikes, a union leader has warned.
Roz Foyer, general secretary of the STUC, said school support workers had “no choice” but to take action later this month to get a fair pay deal.
The three major council unions rejected the latest offer and set a deadline of Wednesday for an improved proposal.
Council body Cosla has insisted the current offer is strong.
Meanwhile, ministers said they had already provided additional funding.
Local authority leaders are to meet on Tuesday to discuss the next steps in the pay dispute which threatens to close schools in all but six of Scotland’s 32 council areas.
Ms Foyer was speaking on BBC Scotland’s The Sunday Show days after three unions agreed to strike over pay and conditions for janitors and school support workers.
The actions are due to take place on 26, 27, and 28 September.
Ms Foyer told the programme she understood parents’ frustration.
But she said the blame did not lie with the workers and compared the current situation to the NHS disputes and teacher strikes, which ministers settled earlier this year after making revised pay offers.
Ms Foyer said: “We have Cosla and the Scottish government making the same mistakes in the same situation with the same dispute as we had last year.
“At the end of the day if you want to avoid workers feeling forced down the road of taking strike action in a cost of living crisis then you need to put a reasonable offer on the table.
“The unions have been waiting for five months for a reasonable offer to be forthcoming. It hasn’t been and inflation is still really high and workers need a decent pay offer.”
Cosla said the two-part plan would give workers at least a £1,929 increase in annual salary by 1 January 2024.
First Minister Humza Yousaf previously said he had already provided Cosla with additional funding to help negotiations in the pay offer.
He added that he hoped that this would be enough to strike a deal.
Three unions are involved in the dispute: Unison, the GMB and Unite.
All three had to ballot each council area separately. This has led to a complex picture of who has the right to strike across the country.
Only six out of Scotland’s 32 councils will be unaffected. These are the areas where the unions did not win a mandate.
They are Argyll and Bute, East Ayrshire, East Lothian, Midlothian, Scottish Borders and West Lothian.
The unions expect the actions to lead to widespread school closures and disruption.