London Underground staff balloted over strike action
London Underground workers will be balloted for strike action over 750 job cuts and ticket office closures.
The Rail, Maritime and Transport (RMT) union said it would "fight" against the plans for all ticket offices to close.
London Underground (LU) said customers and staff were at the centre of improvements to the Tube.
The RMT has to hold a two-week ballot and give Transport for London seven days' notice before any strike action takes place.
Ticket office closures and plans for 24-hour services were announced last week by London Mayor Boris Johnson.
The plans involve the loss of 750 jobs, although London Underground said it would seek to avoid compulsory redundancies.
RMT general secretary Bob Crow said: "It is absolutely clear that the attack on staffing levels and passenger services would have a devastating impact on Tube safety, with assaults and thefts soaring through the roof.
"It is also clear that the most vulnerable members of our society would be most at risk when it comes to both violence and access to Tube services.
"As a result, RMT can confirm that the union will be serving notice today for a ballot for both strike action and action short of a strike with the ballot closing in January.
Phil Hufton, London Underground's chief operating officer, said: "Our commitment is that all Tube stations will remain staffed at all times when services are operating.
"In future there'll be more staff in ticket halls and on gatelines [barriers] to help customers buy the right ticket and keep them safe and secure.
"We're clear that there'll be a job for everyone at LU who wants to work for us and be flexible, that we'll make these changes with no compulsory redundancies."
Tfl is facing a budget reduction of about £78m in the financial years of 2013 and 2014 and said the plans would help it save more than £40m a year.
Earlier Labour MPs Jeremy Corbyn and John McDonnell tabled a Commons motion claiming the plans to close ticket offices would lead to a worse service for passengers.
They said the changes would disadvantage disabled travellers and threaten the safety and security of vulnerable groups such as women travelling at night.