Mayor Bill de Blasio's legal bills are big — and he's relying on city taxpayers to pay for almost all of them at a cost of more than $2.6 million.

On the heels of firing the city's top watchdog, NY1 learned Tuesday that Mayor Bill de Blasio has made another highly unusual move: Overriding the city comptroller's decision to reject a high-profile contract. The contract allows the mayor to use more than $2.6 million in public money to pay the bulk of his legal bills from an earlier investigation by the U.S. Attorney's office into his political activities.

Newly-released documents show the comptroller's office reviewed the city's contract with the mayor's lawyers and rejected it earlier this year. It had questions about the billing, and the office demanded an explanation of what was being done "to ensure that the City is only being asked to pay for expenses/legal fees…relating to the investigation of the Mayor for acts done within the scope of his public employment." The mayor has previously said no public money will go toward legal expenses related to his political work.

During his first term in office, federal prosecutors investigated de Blasio for alleged pay-to-play politics. He was never charged with any wrongdoing.

It's not the first time the mayor's office has overridden the comptroller and executed a contract without his office's approval, but the move is still highly unusual.

"New Yorkers deserve to know how their money is being spent," said Ilana Maier, the press secretary to City Comptroller Scott Stringer. "Our office asked important questions in an effort to ensure that no public funds were used to cover legal fees incurred by the Mayor in his personal capacity, and we are disappointed by the city's decision in this matter."

City Hall defended its decision.

"The Law Department painstakingly verified and appropriately categorized the legal work that was government-related and the work that was not," said Eric Phillips, Mayor de Blasio's press secretary.

In addition to the $2.6 million the mayor is billing the city, he also owes his attorneys about $300,000 from their legal work connected to his political activities.