Hundreds of thousands of council workers are due to start voting on whether to take strike action in protest at a 2.45% pay offer.
Unison is balloting 850,000 local government workers in England, Wales and Northern Ireland on whether to launch a campaign of industrial action, with the result due next month.
Heather Wakefield, the union's head of local government, said Unison members were "disappointed and angry" over pay.
She added: "Four years of real pay cuts have left them choosing between putting food on the table or heating their homes this winter.
"Costs of all the basics are running high. Bread is up a massive 44%, petrol 21% and mortgage costs 8%. For 60% of our members this offer means a pitiful £7.50 per week.
"By voting for a strike, Unison members can send a clear message to the employers that pay is an issue that will not go away. The employers must realise that world-class public services cannot be run on empty stomachs."
Workers covered by the pay claim include care home and home care assistants, housing and environmental health officers, refuse collectors, librarians, nursery nurses, lollipop ladies and school cooks.
