Federal regulators have opened an investigation into nearly 1.3 million Ford F-150 trucks after consumers complained the vehicle unexpectedly downshifted while traveling at high speeds, causing it to rapidly slow down and increasing the risk of a crash.

Regulators received over 100 consumer complaints about transmission shifting to a lower gear without warning. The investigation affects some Ford F-150s.

The NHTSA is probing claims that some of the trucks suddenly dropped into first gear—to the surprise of the drivers—regardless of how fast they were travelling.