BURLINGTON, Vt. — The Burlington teachers union has voted to go on strike after a year of bitter contract negotiations.

Burlington High School history teacher Fran Brock says the teachers “take the action with thoughtfulness and sadness.”

A strike would not begin before Oct. 20.

The teachers union has rejected the working conditions imposed by the board last month and wants a negotiated contract for the current school year.

The school board chairman said last month that the board had no plans to return to the bargaining table.

The strike would be the first by teachers in Vermont’s largest city since 1978 when teachers were on strike for six days.