An eight-day strike by power control room staff at London Underground is due to begin later today.
Rail, Maritime and Transport union (RMT), Unite, and Transport Salaried Staffs’ Association (TSSA) members are due to walk out at 8pm until 7.59pm on July 9.
The dispute is about pensions, length of service, working conditions and the futures of the staff who supply the power to the entire Tube network.
Mick Cash RMT acting general secretary said: "This dispute is over an all-out attack on the power control grade that would damage the futures of this key group of Tube workers.
“Management’s claim they can run the system without them is both provocative and dangerous.
"These staff are effectively the national grid for London Underground and this action will have the most severe consequences for Tube operations but has been forced on us by management wrecking the earlier talks.”
Richard Jones, London Underground's head of command and control, said: "Due to detailed planning there will be no visible impact on the network should the strike action go ahead."