Tube engineers are to stage a second 24-hour strike this month and again threatening services on the Northern, Jubilee and Piccadilly lines.
It will begin at 6am this coming Friday and last until the same time on Saturday.
Any breakdowns during that time could take longer to repair.
The strike - in a long running row over pensions - also includes the Emergency Response Unit (ERU,) the go-anywhere squad which attend across the network to breakdowns and stranded trains
In April the RMT union staged a 72-hour strike in the same dispute.
The strike earlier this month added to disruption on the Jubilee line when a cracked rail was discovered near Canary Wharf during the morning peak.
Transport for London (TfL) was also forced to halt large scale weekend engineering work on the Northern Line and may have to do so again this coming weekend - adding to delays in upgrading the service.
The dispute concerns hundreds of staff working for Tube Lines, the former private sector consortium which has now been taken over by TfL but the name has been retained.
Union bosses say the pension and benefits are not as good as enjoyed by other TfL staff.
This is denied by Jon Lamonte, Tube Lines chief executive, who said: "Further industrial action on the Jubilee, Northern and Piccadilly lines on this issue is completely unnecessary.
"Since becoming part of TfL all Tube Lines employees have kept their existing terms and conditions of employment."
Bob Crow, the RMT leader said: "This dispute is about fairness and equality, nothing else.
"Tube Lines is now a wholly owned subsidiary of TfL and there is simply no excuse for refusing equal pension and (travel) pass rights."
