San Francisco's Board of Supervisors and Mayor Gavin Newsom, are facing a showdown over how the city deals with illegal immigrant minors arrested on felony charges.

Newsom has vetoed a measure that supervisors passed Tuesday that would prohibit local authorities from turning over minors to immigration officials until the minors have been convicted.

Supervisors have vowed to overturn the veto.

The mayor had ordered a change in the city's sanctuary policy in 2008 after Edwin Ramos, an illegal immigrant, was charged with the fatal shootings of a man and his two sons.

Ramos had been charged with felonies as a minor, but the sanctuary policy prevented him from being deported to his native El Salvador.