PORTLAND —  Nine of Portland Public Schools’ buses will have remediation work to fix an issue with seats as soon as next month.

The work comes as part of a voluntary recall, announced last month by the National Highway Traffic Safety Administration. Seats on some ThomasBuilt buses have insufficient impact absorption in the event of an accident.

“It does not require these buses to be taken off the road,” Superintendent Xavier Botana said at last week’s School Board meeting.

Daimler Trucks North America, the manufacturer of the buses, “will install additional impact material between the re-bond back and the vinyl back cover to increase the amount of absorption, free of charge,” the NHTSA said.

Botana expects the remediation work to begin in early December.