The RMT said job cuts would turn stations into "a muggers' paradise"
Thousands of Tube workers are to be balloted for strike action in a row over job cuts.
The Rail, Maritime and Transport (RMT) union said the move was over London Underground's (LU) refusal to withdraw plans to axe 800 jobs.
The RMT's general secretary Bob Crow said the cuts would turn Tube stations into "a muggers' paradise".
LU director Richard Parry said: "The threat of strike action by the RMT is unjustified and kneejerk."
Earlier this month LU said it planned to make the cuts to save £16m a year but ruled out compulsory redundancies and said it would look at redeploying staff.
The job cuts would include 100 managers, 450 ticket office posts and up to 200 other jobs but would not involve closure of station ticket offices, LU said.
The union said it would host a public meeting about the cuts on Wednesday.
About 10,000 Tube workers, who are members of the union, are expected to vote over strike action.
Mr Crow said: "We have already warned that the cuts that are being planned by TfL will turn Tube stations into a muggers' paradise and we now have concrete evidence that the company are speeding up the process and are already leaving stations unstaffed, or babysat with just one member of staff, without any consultation.
"That is a scandalous dereliction of duty and it is only a matter of time now before TfL and [London Mayor] Boris Johnson have a tragedy on their hands as a result of their cavalier disregard for public safety.
'Value for money'
"RMT has made it clear right from the outset that we will not sit idly by while the mayor, his transport officials and Tube Lines drive down Tube staffing levels to dangerously low levels.
"We gave LU and Tube Lines an opportunity to pull back from these cuts but they have decided to plough, on leaving us with no option but to organise ballots."
Mr Parry said: "The changes we are proposing are vital to ensure we can deliver a safer, more frequent Tube service in future.
"The threat of strike action by the RMT is unjustified and kneejerk at this very early stage of the consultation process.
"We have made it clear from the very beginning that all stations will continue to be staffed at all times, all stations with a ticket office will continue to have one and there will be no compulsory redundancies.
"Like any public service we have to be as efficient as we can, particularly in the present difficult economic times, to deliver value for money for the fare-payers and taxpayers who fund the Tube."