The Unison and Unite unions have voted by 80 percent to reject pay cuts at Southampton council.
Unison has 2,300 members at the council and Unite 750.
The unions are now calling on the council to drop its plans or face “the most serious industrial action the city has ever seen”.
Unison branch secretary Mike Tucker said, “Imposing the pay cuts will cost the council tens of thousands of pounds.
“Council workers have spoken. The turnout in the ballot is higher than in the local elections which put the Conservatives in control of the city.”