The RMT said is was an unacceptable attack on DLR staff
Workers on London's Docklands Light Railway (DLR) are to be balloted for industrial action in a row over a new roster system.
The Rail Maritime and Transport Union accused the rail operator of imposing new shifts which, it said, would deprive staff of a number of rest days.
The ballot will close next week, when the union will decide its next move.
Serco Docklands, which operates the service, said the roster changes were to improve safety and reduce fatigue.
But the RMT general secretary Bob Crowe said: "This is a straightforward and unacceptable attack on our DLR members' working and family lives."
A spokesman for Serco Docklands said: "The roster is being reviewed to reduce fatigue, increase handover times between shifts and increase time for training.
"These changes are being implemented to increase safety in the control centre, which controls the movement of DLR train services, in light of the significant growth of the railway.
"Serco Docklands' management team has been consulting with affected staff over recent months and most staff accept the need for a new roster."