The MTA's trying to get more money from the City Council for its Subway Action plan to improve service underground.
Chairman Joe Lhota made a rare appearance before lawmakers Thursday to ask that the city pay for half of the $840 million plan.
Mayor de Blasio has already said the money should come from the state, not the city.
Lhota told the council the mayor's objections could jeopardize the plan's goal of reducing subway delays.
"The benefits of this plan as strong as they are to date, have been muted and we will be unable to implement to implement the plan as quickly as we envisioned it," Lhota said.
City Council Speaker Corey Johnson said any additional city funding should come with more city oversight of the MTA.