The Canadian Union of Public Employees said its membership voted on Sunday to reject the board's latest offer.
Close to 20,000 students attend schools operated by the Chignecto-Central Regional School Board.
About 17,000 of them normally take the bus, but starting Monday morning, parents like Ken Beamish will have to make other arrangements.
"My oldest, he has about a 40-kilometre drive to school so, yeah, it's going to be a lot of travelling there for a bit,” he said.
High school students start writing exams Monday morning.
School board spokeswoman Debbie Buott-Matheson said contingency plans are in place.
"Obviously health and safety is a priority. Our cleaning teams will be working to make sure that our schools and offices are maintained at that level,” she said.
Schools will open an hour before class starts and only an hour after the last bell. All extracurricular activities are cancelled and school space is no longer available for non school-related groups after hours.
The sticking point is the school board's decision to contract out some work.
"I don't know if it had to go this far or not. I would say to get where we want to go, we do have to fight for our rights,” said maintenance worker David Lynds.
The school district covers a large area including Truro, Stellarton and New Glasgow.