The government has announced Tube staff will fall within the explanation of “important services” which have to meet stricter conditions for imposing.
Unions representing Tube workers will have to meet minimum doorways of turnout and support in order to strike.
The change was welcomed by Conservative mayoral possibility Zac Goldsmith, who said it would avert “spurious” action.
Labour entrant Sadiq Khan claimed the move had been timed to “destabilise” bargains over the Night Tube.
A series of Tube walkouts had been proposed for dates in January and February, but Aslef, the Transport Salaried Staff Cooperative and Unite have all agreed to suspend the action.
Rail, Maritime and Move union reps will make a decision on Monday.
Ballots currently make a simple majority to back action.
But under the Trade Union Bill currently in preference to rliament, ballots in core services would need to attract a ap rel of 50% or more – with at least 40% voting in favour – in correct to be deemed lawful.
The government has now signalled its intention to include Underground, bus and handicap drivers, conductors, guards and safety staff under those commands.
However, the strikes which took place in the capital last year ss on have met those conditions.
RMT General Secretary Mick Cash accused the guidance of “trying to ban strikes by the back door”.
But Employment Minister Nick Boles delineated the thresholds as “fairly balanced” with the right to strike.
Mr Goldsmith called the Tube service as “essential” and said the new criteria for industrial action purpose help avoid “strikes on spurious grounds with little genuine support”.
Firefighters, doctors, nurses, border control staff and advisors at state schools will also be considered “important services” underwater the government’s scheme.