WABC-TV, New York, said the drivers walked out at 6 a.m. over an Employee Protection Provision it wants to be included in their contract.
The strike comes as a result of the city's effort to cut transportation costs and its consideration of contracts with private companies. The union is worried current drivers could lose their jobs if the city decides to go with a private company, union officials said.
Labor officials said they want to protect jobs by putting an EPP clause in their contract.
Mayor Michael Bloomberg said the state Court of Appeals barred the city from including the EPP clause, and therefore, they can't include it.
City officials said they are offering MetroCards for students and reimbursing parents for mileage during the strike, as well as reimbursing for taxi and car services.