The strikes are being called in a row over safety
A 72-hour strike on London Underground is planned by rail unions in a row over safety.
A strike from 1830 BST on 6 April to 9 April is planned by the Rail Maritime and Transport (RMT) union and Transport Salaried Staffs Association (TSSA).
The unions claim standards are at risk from plans to close 40 ticket offices and reduce opening hours.
But Transport for London (TfL) said the issues had nothing to do with safety and there was no reason for a strike.
Union members voted in favour of industrial action, which would end at 1830 BST on 9 April, hitting rush hour services and affecting Tube travel.
The unions, which represent 7,500 station staff and drivers, have concerns about staff working alone and plans to introduce "mobile supervisors" at stations.
They said London Underground's plans amounted to "an unacceptable attack on safety standards".
Bob Crow, general secretary of the RMT, said: "Tube workers will not stand idly by while the security of the network is compromised by managers who clearly believe that staff and passenger safety can be looked after on the cheap."
TSSA general secretary Gerry Doherty said: "This is a dispute about the safety of our Tube system.
"The last people we want to hit are the travelling public but this seems to be the only way we can make LU listen."
LU spokesman Howard Collins said industrial action was "totally unnecessary".
"We believe we have resolved some of the small safety concerns that the trade unions have," Mr Collins said.
"This is not about reducing staff, we have staff on our stations. This is not about anything to do with safety whatsoever."
He said LU would do "all we can to keep London moving" if the strike took place, but added: "Our main focus is to resolve the issue."
Talks between the unions and LU continued on Friday, with further talks planned next week.
British Chambers of Commerce director general David Frost said that, coupled with chaos at Heathrow's new Terminal 5, the Tube strike plans sent out a signal that "London is not a place to come and do business".
He added: "Enough is enough. Someone needs to get a grip and sort out the mess that the UK's transport infrastructure has become."