Liberal Democrat London assembly member Caroline Pidgeon has hit out at the Rail and Maritime Union (RMT), calling maintenance firm Tube Lines' offer of a 4.85 per cent pay deal "generous".
The deputy chair of London Assembly's Transport Committee accused Bob Crow, the general secretary of the RMT, of "living in the past" and called on the mayor of London Boris Johnson to support Tube Lines.
She said: "The dispute is politically motivated - Bob Crow wants Tube Lines trashed.
"We can't be held to ransom by a militant union. Tube Lines and their workforce need to stand firm in resisting strike action."
The Liberal Democrat's comments follow the RMT union's ballot of 1,000s of its members working at Tube Lines on the possibility of strike action.
Former mayor of London Ken Livingstone had promised RMT members during his election campaign that they would be able to join the London Underground pension scheme.
RMT members are now looking to Boris Johnson to follow this commitment up.
During his own electoral campaign, Mr Johnson unsuccessfully tried to close a deal with unions that would prevent them taking strike action and in return an independent arbitrator would run pay negotiations.
So far, the RMT has rejected a pay offer of 4.85 per cent on a one-year basis and a two-year deal at 4.95 per cent.
Earlier this year, Network Rail employees settled for a 4.9 per cent deal with Tube Lines and London Underground workers accepted a 4.6 per cent offer.
Tensions between the RMT, the London Underground and its contractors have been exacerbated over recent months following reports of unfair sackings and an increase in complaints from workers about bullying and harassment.
Mr Crow said: "There are people being treated appallingly and each of these issues needs to be sorted but if they are not we will look to co-ordinate strike action to make sure they are."