Hundreds of thousands of council and school staff in England, Wales and Northern Ireland have started voting on whether to strike over pay.
Unison said most workers - including refuse collectors, teaching assistants and social workers - have been offered a below inflation 1.75% rise.
It equates to 2.75% for those on the lowest wage level, Unison claimed.
The union is recommending its members back industrial action in the ballot.
'Undervalued'
Earlier this year Unison submitted a joint pay claim with other unions for a wage rise of least 10% for all council and school support employees.
Unison’s head of local government Mike Short said: “Council and school workers have gone the extra mile throughout the pandemic, keeping schools open, ensuring communities are safe and providing essential services. often at risk to their own health.
“This inadequate pay offer shows they’re undervalued, particularly with the cost of living being ramped up. They should be given the credit they’re due and rewarded properly.
“It’s still not too late for the employers to do the right thing by making a decent offer to avoid strike action. The Government should also play its part by providing the necessary funds.”
Earlier this year Unison, Unite and the GMB came together to fight for a bigger pay rise - describing how council and school staff deserved more after working though the pandemic.
A spokesman for the local government body Cosla - which works with the Scottish Government and other key partners - previously said the offer "remains on the table".
The spokesperson said: “We have made an offer to our trade union colleagues.
"This offer remains on the table whilst we continue with on-going constructive negotiations.”
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