The threat of a Tube strike escalated today as 10,000 staff began a ballot in a dispute over pay.
Members of the RMT union, including drivers, will vote and are expected to endorse a strike call. The ballot result is due at the end of the month.
Union leaders at the RMT and Aslef have rejected a four-year pay deal. They have agreed to meet London Underground management at conciliation service Acas next Tuesday but there is no new deal on the table.
More than 2,400 Tube drivers belonging to Aslef will conclude their own ballot later next week and are also forecast to back strike action.
The first combined stoppages by the unions could begin in mid-April.
Transport for London said the pay deal guarantees above-inflation rises. RMT leader Mick Cash said LU had “failed to come up with an offer that would fully recognise the efforts of their workforce day in and day out”.
Southeastern commuters suffered major disruption today as engineers checked tracks between Dover Priory and Folkestone Central after rocks fell following torrential rain yesterday.
