Transport workers on the Docklands Light Railway (DLR) are balloting for strikes over attacks on pay and conditions.
The RMT union members say there has been a breakdown of industrial relations on the DLR, which is run by Serco. The ballot ends on Thursday of next week.
RMT union members on the London Underground are also balloting for strikes against a massive cuts programme.
Bosses want to slash up to 1,000 jobs, cut pay for remaining workers and close ticket offices.
The ballot ends on Friday of this week.
Jarvis workers put in dismissals claim
Rail workers sacked when rail company Jarvis collapsed in 2000 have a claim for unfair dismissal, an employment tribunal ruled in December.
There will be a further hearing in early March in Leeds to decide the value of the unfair dismissal claims.