WESTBROOK, Maine (NEWS CENTER) -- Nine school buses are off the road in Westbrook after it was discovered that their inspection stickers were expired.

The school department's Director of Operations, Dean Flanagin, says he received a call from State Police who said they got an anonymous call from a resident about buses operating in Westbrook with expired inspection stickers.

Officials found nine total stickers that were not up to date, six route buses and three reserve buses. A few of the stickers had just expired in May, but others had been expired for up to four months. The department was told to pull all buses without up-to-date stickers off the road until they could be serviced.

By law, school buses are required to be inspected every six months.

Flanagin says the school department knew that some of the buses were due to be checked, and they were working to get them scheduled. He says missing the inspections was a scheduling lapse, and even though the sticker isn't up to date, drivers check every day to make sure their buses are safe.

But others say this shouldn't have been missed at all, and it's a major mistake that could've been costly.

Tom Goughnour says he put stickers on Westbrook buses for the last 3 decades as a mechanic for the school department. He retired last August but says the stickers he put on were still on some of the buses.

He says he noticed the sticker were expired, and he wasn't the only one.

"I had a driver stop me and tell me the inspection was out," says Goughnour. "He says, 'I was told to drive it.' I said, 'You are kidding me.'"

Flanagin says he was not aware of any drivers coming forward to report that their bus' inspection sticker had expired, but also said they are not at fault for what happened. The school department is working on creating an automated system to ensure their buses do not have expired inspection stickers.