The countdown is on to a potentially significant disruption in New York City’s yellow school bus service, with bus companies threatening to shut down if they don’t get a new contract.

It wouldn’t be considered a traditional strike. The companies involved, and there appear to be at least three of them, would shut down. That could prompt driver layoffs and service disruptions as early as Monday.

The companies have been operating without a contract since the summer, relying on month-to-month extensions. Those extensions expire Friday, which could leave tens of thousands of kids without bus service.

The panel didn’t vote on a new contract at a jam-packed meeting on Wednesday night. They say they want bus service improved before they agree to a new deal, and rejected a 5-year deal currently on the table.

The law firm negotiating for the bus companies says the current proposal calls for improvements like enhanced GPS and call centers with real-time parental help, investment in more than 200 electric vehicles and more investment in employee training.

Some bus companies that service New York City schools have agreed to another month-long extension, which means there will be some bus service next week. It’s unclear which routes would be affected.

Melissa Aviles-Ramos, the NYC schools chancellor, said more than half of the vendors had signed those emergency agreements. She said students with disabilities would have priority when it came to busing.