The United States government is investigating reports that tailgates are falling off the back of General Motors pickup trucks without warning.

Such investigations can lead to recalls.

According to Associated Press (AP), the investigation could potentially affect thousands of vehicles. The National Highway Traffic Safety Administration reportedly is looking at the GMC Sierra from model years 1999-2002; the Chevrolet Silverado from model years 1999-2003; the 2002 Cadillac truck and the 2002 Chevrolet Avalanche.

According to AP, NHTSA said US owners have reported numerous injuries due to the alleged defect – in one case, a tailgate separated from a moving vehicle and, in another, the tailgate broke as a consumer was loading an all-terrain vehicle onto his pickup. The ATV fell on him and broke his shoulder.

NHTSA said it appears that support cables can break due to metal fatigue, but consumers can’t see if they’re worn because they’re covered with a protective plastic sheath, Associated Press added.