document: Members of the RMT and TSSA unions backed industrial action following a similar vote by drivers.
  Workers in these unions will now join a planned 24-hour walkout by members of the drivers' union Aslef, which begins at 21:30 BST on 8 July.
  Talks aimed at averting a strike are being held at the conciliation service Acas.
  The RMT union and TSSA said its workers planned to begin striking at 18:30 BST.
  The unions are in dispute with London Underground over pay and conditions for the new all-night Tube, which is due to start at weekends from mid-September, on sections of the Central, Jubilee, Northern, Piccadilly and Victoria lines.
  The RMT said its members voted by 91% in favour of strikes and 96% for other forms of industrial action.
  The union is also in dispute over a series of other issues including jobs and safety.
  RMT General Secretary Mick Cash said: "The industrial relations situation on the Tube has sunk to an almost unprecedented low with all four unions united and balloting for action over pay and working arrangements due to be ushered in under the guise of the mayor's 'night Tube' vanity project in just 10 weeks' time."
  TSSA General Secretary Manuel Cortes said: "We hope that this result will show Boris Johnson just how angry our members are at his plans to try and rush the start of the night Tube without any detailed agreement on manning levels."
  Among TSSA members, the vote in support of strikes was 76%, with 88% backing other forms of action in a turnout of 44%.
  London Underground's chief operating officer Steve Griffiths said: "Londoners and businesses overwhelmingly back the Night Tube.
  "It will make life easier for everyone, cut journey times, create jobs and boost the economy.
  "No-one is being asked to work more hours," he added. "In return, we are offering a realistic pay increase this year and next, as well as an additional payment for Night Tube working. "
summary: More London Underground workers have voted to strike in a dispute over the new all-night Tube service.