Thousands of city students could soon be left without a way to get to school. 

Members of a school bus drivers' union voted overwhelmingly last night to authorize a strike as soon as Tuesday.

It affects more than 850 employees of Jofaz Transportation and Y&M Transit.

After months of negotiating, talks broke down between Teamsters Local 553 and the two companies, which are owned by the same person.

They carry thousands of students on 600 routes in Brooklyn, Queens and Staten Island.

Union members say the companies are forcing workers to pay for future health care cost hikes and only offered some employees a raise. 

They say many of the bus drivers make minimum wage and cannot afford the extra costs. 

"We need to have better wage increases and everything else. Our medical insurance was going to go through the roof. We can't afford that. Our salary doesn't warrant that," said Lisa Cilone, a driver with Y&M Transportation. "We never had to pay for our medical. That was already paid for us as part of our pay. But now, they want us to pay every week."

The Department of Education says it's disappointed with the vote. 

It says it will offer either a MetroCard or alternative bus service for students if necessary.

The bus companies did not comment.