Unite plans to ballot four UPS depots across London for industrial action, extending the dispute that began at the parcel firm’s Camden depot last year.
It will ballot members in Croydon, Feltham, Dartford and Barking.
Unite has also accused UPS of “victimising” two union reps at Camden- one of which has been suspended by the firm.
A UPS spokeswoman said: “Discussions with Unite are currently on-going, and we remain hopeful that a mutually satisfactory agreement can be reached.”
“It is UPS’s policy to comply with all laws governing employment and labour practices worldwide, and UPS is careful to take into account the point-of-view of unions along with the interests of our customers, our employees, our shareholders and our company as a whole,” she added.
The union held a one-day strike at Camden in November, claiming drivers and loaders at the depot were being forced to handle unreasonable workloads.
Unite also alleged that UPS made staff work several hours beyond their finish times or face disciplinary action.
The two parties have been in talks since November, with the next meeting scheduled for 30 June.
Unite regional officer Onay Kasab said: “This morning [25 June] our rep was suspended on the most spurious of grounds. Another rep faces disciplinary action for failing to deliver his overloaded workload - he was set up to fail.
"Enough is enough. We will now begin making preparations for a strike ballot which will include UPS depots across the capital.”