Binmen in Birmingham could go back on strike after they accused city council bosses of failing to deliver promises.
Refuse collectors were involved in a bitter four-week dispute with managers over pay last year which left mountains of rubbish piled high at the roadside.
Residents in the worst-affected neighbourhoods saw bin bags line their streets for as long as six weeks as the walkout and icy weather took their toll.
Union leaders said the council has broken the terms of a deal which was signed in March and is understood to relate to complex terms for shift allowances and overtime pay.
Unite regional office Lynne Shakespeare said: “This is incompetence of the highest order.
“If this agreement is not implemented, we shall be forced to meet with our membership again and possibly restart the strike action.
“The council has made no attempt to honour the agreement which we all signed in March.
“It seems that the council enjoys being in dispute and seeing tonnes of rubbish on the streets, especially during the summer months.
“If the council did not want to reach an agreement, why did they bother to make one with us – it all seems to have been a complete waste of time.”
A Birmingham City Council spokesman said: “The city council is fully committed to implementing the agreement that was agreed in March.
“Any talk of further strike action is disappointing as the city council is honouring it’s commitments under the agreement and is clearly engaged in a process so as to ensure that employees’ contracts are changed by the correct legal process.”
The city council will be keen to try and avoid a repeat of scenes last December when bin men staged a one-day strike and impose work-to-rule measures.
Hiring an army of casual staff to clear the backlog cost the city thousands of pounds.
Further strikes were avoided in January after a last-minute verbal agreement.
An deal was eventually ratified by two thirds of union members and signed in March but Unite said that the council had “reneged” on certain elements.