Local government employers have made it clear a two-year pay offer is "final" after union leaders recommended rejection.
Unison officials narrowly voted against a proposed deal of a 2% rise for most council and support staff in England, Wales and Northern Ireland from April and a further 2% in April 2019.
Lower-paid staff were offered a higher wage rise of up to 16% over the two years.
Unison's head of local government Heather Wakefield said: "Unison's national joint council committee has today voted narrowly to reject the local government employers' two-year pay offer for council and school support staff.
"The union will now begin to consult with its members across local government in England, Wales and Northern Ireland to seek their views. That consultation will begin on Monday and end on March 8."
Sian Timoney, who chairs the National Employers Side of the National Joint Council for Local Government, said: "The employers are extremely disappointed that Unison will be advising its members to reject the pay offer. The employers have been very clear that the pay offer is a final offer.
"The employers believe that the offer is fair for all staff and includes substantial increases for our lowest paid staff as well as meeting the challenge of the national living wage by introducing a new pay spine in 2019."
Unite is recommending rejection of the offer among its members.