Councillors spent more than seven hours on the last Wednesday in June deliberating over Mayor Wu’s vetoes, and just one override went through, a proposal from District 3 Councillor Frank Baker to fund a salary increase for municipal security officers.

The override, which mustered support from more than two-thirds of the City Council, set aside $584,000 for that purpose, out of a $4.2 billion operating budget for fiscal year 2024, which started July 1.

The only problem, Wu said in a letter released this week, was that the move contravened city and state law, because councillors were inserting themselves into collective bargaining between labor officials working for Mayor Wu and the security officers.

Wu told the councillors that she’ll ignore the override, pointing to the section of the city charter that prohibits councillors from getting involved in labor matters and contracts, as well as a section of state law that excludes third parties, such as the council, from participation in collective bargaining.

Referring to the Municipal Police Patrolmen’s Association, Wu wrote, “Both the City and the Union agree that MPPA salaries should be adjusted, but the parties have yet to reach agreement on the size of the increase.” She added: “There is no other interpretation of this override vote than as a directive from the City Council to the Administration to adopt the MPPA’s specific salary increase demands in bargaining, which is a clear cut violation of the City Charter and state law.”

Councillors can vote on the appropriation of funds once negotiations are complete and the contracts are settled, but not before.

The letter closed the books on the second year in a row that the councillors, with expanded budgetary powers handed to them by voters through a 2021 ballot question, seemed unable to use them without breaking the law or violating the city’s charter.

The Council had the power to amend $1.8 billion, or 42 percent of the budget, but only if its final total didn’t exceed what the mayor proposed. Before the voter-approved charter amendment, councillors could only sign off on, reject, or reduce whatever the mayor proposed.

Some councillors made an attempt this year to cut the Boston Police Department’s budget. A similar effort last year was shot down by the mayor, as was this year’s. Wu called the attempt “illusory” because the city is required to pay out salaries and overtime.