ST. PAUL — Gov. Mark Dayton has vetoed a bill that would have let schools lay off teachers based on their performance rather than simply on seniority.

Dayton vetoed the bill Thursday. In his veto letter, the Democratic governor says the bill shows prejudice against public schoolteachers. He says it replaces the most prevalent system of determining teacher layoffs with what he called “vaguely formulated ideas.”

Under current law, schools must only consider seniority in layoff decisions. The only exception is districts that negotiate their own local policies.

The bill’s chief House sponsor, Republican Branden Petersen of Andover, says he tried to work toward a bill Dayton would sign but made no progress after four separate meetings with the governor. He accused Dayton of siding with union special interests over students.