Consumer watchdog group Center for Auto Safety (CAS) issued a petition to NHTSA in order to investigate certain Hyundai and Kia models following complaints of spontaneous fires unrelated to car crashes.

“These complaints reveal a frighteningly large number of vehicles manufactured at the same time catching fire. Altogether, more than 2.2 million of these vehicles were manufactured during model years 2011-2014,” said CAS.

The group adds that there have been 120 consumer complaints on non-collision fires submitted to NHTSA and 229 separate complaints of melted wires in the engine bay, smoke and burning odors, pointing at a large number of models manufactured at the same time catching fire.

The models in question are the 2011-2014 Kia Sorento and Optima, as well as the same period’s Hyundai Sonata and Santa Fe. Center for Auto Safety says that altogether more than 2.2 million of these models were manufactured during model years 2011 to 2014.

The 2011-2014 Kia Sorento, Kia Optima and Hyundai Santa Fe models were manufactured in the company’s Georgia plant while the Hyundai Sonata models were built in Montgomery, Alabama.

“Unfortunately, most, if not all, auto manufacturers occasionally produce vehicles that catch fire, even when not involved in a collision,” said Jason Levine, Executive Director of the Center. “However, when these Kia and Hyundai vehicles are compared to other similar vehicles that were manufactured at the same time, there is enough of a statistical disparity to suggest a systemic issue that NHTSA must investigate and seek a repair remedy as soon as possible.”

In one of the complaints to NHTSA, a 2012 Hyundai Sonata owner said his car was engulfed in flames after sitting parked for an hour outside a store. A fire investigator said that an electrical short in the wiring harness caused the wires and tubes in the engine compartment to melt and drip on a pile of leaves which started the fire.

NHTSA is required to respond to a petition of this type within 120 days, according to Center for Auto Safety.