Unless the MTA can shore up billions in city or state money, the transit agency will have to cut its budget or borrow money — either of which state Comptroller Tom DiNapoli argued can hit straphangers hard.

"If the MTA doesn't get the funding it needs, the MTA will have to choose between cutting the size of the capital program or borrowing more," DiNapoli wrote in a statement, "which could lead to less reliable service or higher fares and tolls."

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In his latest report, DiNapoli said a lack of investment by the state and city would jeopardize existing service and expansion products. If the MTA turns to loans, DiNapoli added, it may force the agency to hike fares and tolls.

The total budget gap currently stands at $9.8 billion. The transit agency has spent the last few months lobbying New York City to front $2.5 billion, a big jump from the $657 million it offered in June.

MTA spokesman Kevin Ortiz said the agency appreciates the comptroller's recognition of the challenges the MTA faces while digging into the de Blasio administration.

"While the state is proposing a contribution close to its record high, the city wants to contribute close to its record low," Ortiz said. "Facts are facts, and the facts in this report make clear it is long past time for the city to contribute its fair share to the MTA Capital Program."

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Gov. Andrew Cuomo announced earlier this year the state would commit to $8.3 billion toward closing the gap.

City officials have long argued that the $657 million meets and exceeds the city's usual contribution to the MTA's capital plan — previously $500 million — which helps pay for maintenance existing subway services and new projects.

Mayor Bill de Blasio has been particularly pressured by the state and its allies to boost its contribution. On Monday, the mayor denounced a Transit Workers Union advertisement accusing him of failing riders as "misleading" and "pitiful."

"The state has budgetary responsibility for the MTA," de Blasio told reporters. "All of the dire warnings in that ad should be addressed the state of New York," he said, adding that the city is open to increasing its contribution as long as City Hall has a clearer sense of what the money is going towards.