London Assembly Conservative member Gareth Bacon accused TfL of running "a gold-plated pension scheme" for its workforce, with contributions from the taxpayer six times higher than the contribution of TfL's average employee.
RMT transport union leader Bob Crow responded by saying his union would not tolerate any erosion of workers' rights and agreements.
Mr Crow added: "Any attack on pensions, passes or other hard-won conditions of service would be met with the biggest wave of industrial action on London Underground in 30 years."
Mr Bacon said that figures showed that TfL staff pensions had cost the taxpayer £1.6 billion in employer contributions over the period 2004 to 2011.
During this period, the amount contributed by TfL into workers' pension pots had risen by 54%.
He said that currently the fund was in deficit, so including deficit payments, the employer was contributing over six times the amount of employees.
Mr Crow said: "If members of the London Assembly think that they can play politics with our members' working conditions and benefits on London Underground then they should think again."