The organisation said that if workers back industrial action, there could be mass walkouts across the country in August.
Cosla is said to have made a two-stage offer, which would operate over an 18-month period. It would give a 2.2% increase for the first six months and an additional 2% for the subsequent 12 months, until September next year.
A consultation by the union earlier this month saw thousands of staff employed by Scottish councils vote to reject the offer, with 91% of workers rejecting the pay proposal.
The ballot will continue until 17 July.
‘Council workers deserve better’
Unison Scotland local government committee chair, Colette Hunter, said: “It’s disappointing that it’s come to a strike ballot. But, Cosla has refused to either improve its pay offer or join unions in their call to meet the Scottish government to discuss additional funding.
“Striking is always a last resort, but workers deserve to be paid wages reflecting their essential roles. They’re determined to achieve just that.”
Unison Scotland lead for local government, David O’Connor, said: “Cosla’s proposal falls short of Unison’s pay claim. It’s also less than the offer made to the lowest-paid local government staff south of the border.
“It does nothing to address the impact of below-inflation pay settlements that have reduced the value of staff wages by a quarter over the past 14 years. Scotland’s council workers deserve much better.”
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