ST. PAUL — The superintendent of St. Paul public schools said she is concerned about school safety, but said a plan by the teachers union would cost too much.

Superintendent Valeria Silva responded Wednesday after the St. Paul Federation of Teachers said it would request mediation with the district — a perquisite for a strike.

The issue was raised after staff members were attacked by students Friday at St. Paul Central High School.

Silva said school safety is of “utmost importance” to her.

But she says the teachers’ concerns seem to go beyond school environment and include pay.

The union’s proposals include raises of 2.5 percent a year for each of the next two years as well as ideas for improving school safety.