Rubbish collectors in Birmingham could take more strike action over a contract and pay dispute after rejecting the latest offer from the city council.
Up to 95% of the 500 workers rejected the offer, unions said.
Binmen have staged strikes and also been working to rule for several weeks over a pay dispute which unions said would see them lose £4,000 per year.
The council said it was disappointed as its proposed agreement offered "a positive way forward".
Strikes were suspended during the talks - held over the past few weeks - but now further action could be taken after the binmen rejected the offer, the GMB said.
Roger Jenkins, from the GMB, said it was trying to arrange an emergency meeting with the council on Friday.
'List of cuts'
In a statement the council said: "There is disappointment that despite several weeks of intensive and constructive talks between the council and the trades unions, the unions and their members have rejected the proposals which resulted from these talks.
"The council believes that their proposals offered a solution to the trades unions' industrial action.
"These contained a number of changes brought about directly through the talks with the trade unions, and the council believes the proposed agreement offered a positive way forward.
"The trade unions are well aware that the city council is unable to go any further in amending its proposals due to wider constraints it faces."
A spokesman for Unite said: "On 12 January strikes by refuse collectors in Birmingham were called off following peace talks.
"It was agreed that talks would continue with a view to recommending a successful conclusion to the dispute subject to agreement by both sides and a membership vote.
"The dispute is over an equal pay review by the council which means workers will lose up to £4,000 a year.
"Unite believes that Birmingham city council's latest offer amounts to little more than a list of cuts together with some overtime which isn't even guaranteed."