Workers responsible for fault-finding and maintaining the electrical supply to the London Underground will begin their second 36-hour strike tonight in a row over pay.
Members of the Rail, Maritime and Transport union employed by EDF Energy Powerlink will walk out at 8pm until 8am on Tuesday.
General secretary Bob Crow said: "Despite the overwhelming vote for action and an absolutely rock-solid strike in November, EDF Energy Powerlink has so far refused to acknowledge that shift testers should have pay-parity with their non-shift colleagues.
"Day-work staff rightly received a £3,000 increase for delivering flexibility, and their shift-working colleagues are simply seeking recognition of the flexibility they too have delivered, not least in accepting sweeping shift changes that have disrupted their work-life balance.
"If the company keeps its head buried in the sand we can only conclude that it is more interested in shameless profiteering than in delivering pay justice to committed and highly skilled staff who do a crucial job in keeping London's Tube network moving."
The workers staged their first strike last month.