Transport for London has been blasted for launching an "extensive and expensive scabbing operation" as the network attempts to keep the Waterloo & City Line running in the wake of a 48-hour strike.
The action, which started at 9pm last night, is expected to have "no visible impact". TfL claims just three people voted in favour of the strike, out of six staff who are union members and eight who work in the Waterloo & City control room in total.
London Underground has put "detailed planning" into place that should keep the line, which connects Bank and Waterloo, running throughout.
But these measures have been blasted by RMT's general secretary Mick Cash.
"LU have mounted an extensive and expensive scabbing operation today," he said. "If the company had spent as much time, money and effort in resolving this dispute as they have in trying to break it we could have negotiated a settlement months ago."
In spite of TfL's claim about the ballot, Cash said the service control team was "100 per cent united and solid in their action today as they fight for pay and grading justice".
He added: "All they are asking for is to be treated the same as similar staff elsewhere on the Underground. Their claim is for basic fairness."