The San Francisco Board of Supervisors is considering dozens of measures to place before the voters this November. Along with bond measures, new taxes and zoning changes are charter amendments that will erode a mayor’s ability to manage city government. As former mayors, we urge the Board of Supervisors to stop playing politics with the governance structure of San Francisco.

The proposed charter amendments include the establishment of a new citywide elected official (the office of the public advocate) and the removal of the mayor’s direct oversight of the city’s housing and economic development departments. Earlier this week, the Board of Supervisors voted to put two measures on the November ballot, one that would strip the mayor of his or her full appointment power to the Municipal Transportation Agency Board of Directors, and another that would eliminate the mayor’s authority to appoint to the Board of Supervisors citizens who can stand for election in their own right if a board vacancy occurs.

We recognize that in San Francisco, as a city and a county, there has always been a certain tension between supervisors and the executive wing of city government. To that end, important charter reform approved by the voters in 1995 strove to find a balance between legislative and administrative authority. The Board of Supervisors regained the power to both add and subtract spending in the annual budget, to legislate on almost any administrative matter, and to veto mayoral appointments to virtually every city commission.

On the other hand, and most importantly, the mayor became more accountable for the performance of every city department, merging the functions of the chief administrative officer into a new administrative office reporting to the mayor. Clear accountability of the mayor’s office is essential for our city and county government to work. As a result, San Franciscans know to hold the mayor responsible for the efficient and effective delivery of government services.

Since the 1995 charter reform, members of the Board of Supervisors have continuously tried to chip away at the authority of the mayor. In so doing, accountability among our elected officials has been significantly diffused. But none of those ballot efforts can compare with the outright power grab that could be on this November’s city ballot.

The Board of Supervisors can do the voters of San Francisco a huge favor by reducing the number of ballot measures they may be confronted with this November and start by tabling these unnecessary measures. Call your district supervisors and tell them to focus on governance, not politics, and to maintain our important system of accountability. The alternative is to join us in voting against these measures in November.

Sen. Dianne Feinstein, D-Calif., Frank Jordan, Willie L. Brown Jr. and Lt. Gov. Gavin Newsom are former mayors of San Francisco. Brown is also a columnist for The Chronicle.