Bin collectors based in Birmingham have voted to take further industrial action in a row over pay as residents face mounting piles of rubbish.

Union representatives have confirmed workers will strike for two days on January 13th and 14th. The walkout will add to the disruption to refuse services caused by cold weather, and an earlier decision by collection workers to work to rule from the 22 December.

The dispute in Birmingham centres on the legal duty of UK councils to ensure equal pay for men and women, and the method the council used to achieve this.

Previously, the council introduced an enhancement worth about £4,000 a year to equalise gender pay. However, in 2010 a court ruled that this action was incorrect or “not equality proofed”. Now the council has said it needs to remove the enhancement, which has the effect of reducing pay.

But the GMB and Unite unions representing workers are unhappy that the current pay review will mean that workers such as refuse collectors, garage staff and road sweepers will suffer a pay cut, and has accused the council of ignoring union advice when it made its original decision.

Unite has also accused the council of “escalating the current dispute” by threatening to pay the refuse collectors not by their contracted hours but by the amount of waste collected, and by employing casual workers to clear the build-up of rubbish.

Lynne Shakespeare, Unite’s regional officer, said: “We’ve already told the council that they are spending more effort and taxpayers’ money to break this strike than it would cost to resolve it. The council recruited 200 casual staff to break the strike and it cost the council £20,000 just to provide workwear for them, before any wages and dust wagons are paid for.”

A Birmingham City Council spokesman said: “We are not threatening to change the way our refuse workforce is paid and it is wholly misleading to suggest they are being paid based on how much waste they collect.

“Our refuse crews are paid on a task and finish basis and during their current ‘work to rule’ they are not finishing their daily rounds.

“The industrial action cannot be an excuse for partial performance – so appropriate action will be taken… this is not a permanent measure but one which are using whilst the work to rule and other industrial action is in place.”

And he added: “Discussions are taking place with the trades unions, and they will continue, but it is clear that the City Council cannot simply reinstate the salary reduction arising from the previous incorrect assimilation of part of the workforce without creating a further equal pay problem that will affect another 11,000+ employees in the City Council – and this is unaffordable within the current financial climate.”