INDIANAPOLIS (WISH) — Indianapolis Public Schools is promising to punish bus drivers who skipped work Friday, dropping the district into chaos.

The state’s largest school district had to shut down its bus service, leaving thousands of kids unable to get to school.

Bus drivers called in at the last minute to let IPS know they were too sick to work. The district thinks the drivers were acting out after learning they’d have to reapply as IPS changes transportation companies for the next school year. If that’s right, IPS leaders say the behavior is unacceptable.

“Their lack of concern for the safety of students in elementary through high school in the middle of winter is disappointing,” Superintendent Aleesia Johnson said.

A total of 71 of the district’s 300 bus drivers did not come to work, forcing the district to shut down its 305 bus routes.

The result: no buses for any students, and more than half of the district’s students at home and out of class.

“This mass calloff has denied our most vulnerable children, including many of our students with special needs who require specialized transportation services, their educational opportunity and disrupted the schedules of countless families,” Johnson said.

According to the AFL-CIO, the union did not organize the effort. The union confirmed frustrations with recent decisions made by the district, but said the employees acted independently.

“That is hard,” Johnson said. “We don’t deny that. A transition is always difficult. So I believe that’s the source of some of this, is the frustration that they are feeling of that change that’s coming.”

IPS is calling the absent drivers “rogue” and says they will all be punished for their actions. IPS did not give details.

“Based on our personnel policies and procedures for the number of occurrences those drivers have, there will be disciplinary action accordingly,” Johnson said.

With the time of year, it’s a real possibility that some drivers actually are sick. So, IPS says, they will be thoroughly investigating with their human resources department.

“In that case, there will be calls made to each individual person who called off to be sure we fully understand specifically the context of them not being at work today,” Johnson said.

IPS says they have no plans to change their decision to switch transportation services next school year.