THE BRONX - City school buses were rolling this morning, but it's unclear how long it will last as drivers threaten to step out from behind the wheel.

The union that represents the drivers, Local 1181, has been threatening to go on strike since Mayor Michael Bloomberg proposed a plan to save $1 billion by putting the city's 1,000 bus routes, covered by 52 private companies, out for competitive bidding.

Drivers say they want assurances that the Employee Protection Provision, which protects their jobs based on seniority, will not be eliminated from their contracts.

The Department of Education (DOE) website is warning parents about the possibility of a yellow bus disruption, which could affect more than 150,000 students citywide.

The DOE also says that if a strike does happen, it will issue MetroCards and reimburse parents who drive their kids to school.