London Underground staff are set to stage two more 24 hour strikes this month.
The Rail Maritime and Transport Union (RMT) announced the new strikes this afternoon.
They said that their members will walk out for 24 hours beginning at 9pm on Tuesday 25 August and again from 9pm on Thursday 27 August.
It has yet to be confirmed which lines will be included in the walk out.
The fresh strikes come amid disputes over the introduction of all-night trains, which are due to come in from 12 September.
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In a statement announcing the strikes, the RMT praised staff for "magnificent strike action" in walk outs so far this summer and said they were to be "applauded".
RMT general secretary Mick Cash said: "Our members the length and breadth of London Underground have made it clear that they are determined to protect their work/life balance and not fall into a trap where they will be forced to wreck their home lives in order to comply with the 'rosters from hell' which have been drawn up to plug the staffing gaps in the night Tube plans."
