Mediation between the Mt. Diablo teachers union and school district officials has failed, the union announced recently.

The Mt. Diablo Education Association and Mt. Diablo Unified School District met with a mediator for three days last week without reaching an agreement, union officials said. The process now moves to a fact-finding stage of unspecified duration.

The union is seeking a salary increase of 12.5 percent over three years, according to the news release, in which union officials said teachers will strike if necessary.

The district serves 29,000 students from Walnut Creek, Concord, Bay Point, Pleasant Hill, Clayton, Pittsburg and Martinez.