Mayor Bloomberg’s congestion pricing proposal is facing another obstacle after the speaker of the state Assembly, Sheldon Silver, announced yesterday that he would hold a hearing on how the revenues from the traffic tax would be spent.

Mr. Silver, along with two other Assembly Democrats, Herman Farrell Jr. and Richard Brodsky, both opponents of the congestion pricing plan, will hold a hearing tomorrow to examine the Metropolitan Transportation Authority’s five-year capital plan, which outlines budgets and time lines for expansion projects like the Second Avenue Subway.

The MTA’s executive director, Elliot Sander, who will testify at the hearing, has said Mr. Bloomberg’s plan to charge drivers $8 to enter Manhattan below 60th Street would generate $4.5 billion in revenue, which the MTA could borrow on in advance. Even with the use of congestion fee funds, the MTA budget has a $9 billion shortfall.

Mr. Silver said in a statement yesterday that he is concerned that the congestion plan would not be fully funded and that it is unclear whether the proceeds from the traffic tax would be devoted to capital projects alone or to routine maintenance and operations.

The congestion pricing plan would qualify for $354 million in federal aid if passed by Albany and the City Council by March 31. Mr. Silver has said he would not support it unless it includes rebates for low-income drivers.