The underground workers are furious the government is pushing ahead with tough cost cuts they say could total more than £4bn over three years.
It is thought station and ticket staff are likely to bear the brunt of the cuts. The union also says vital maintenance work will be affected.
The union now has 28 days to decide whether it will stage a walkout that could bring the capital grinding to a halt.
A spokesman for RMT said: “If you start cutting back on these key staff it will impact on the entire system. It won’t just affect our members, it will affect the transport-using public.
“We also fear this is just the first wave of cuts that could badly affect the underground network. We want assurances this won’t happen.”
Members of the union voted 76 per cent in favour of strike action and 88 per cent of action short of striking.
It will now liaise with sister transport union TSSA, which will announce its own ballot result next week.