Gentex, one of the world’s biggest suppliers of rear-view mirrors, had until Friday not ended the job of a single employee since its inception 34 years ago. That record ended when the Michigan-based company said it was letting go of almost 400 people, one-sixth of its workforce.

Gentex depends on General Motors and Chrysler for close to a fifth of global revenues. Although orders from other customers have also shrunk, the job losses at Gentex are a sign of how the squeeze is tightening on suppliers that do business with the two beleaguered Detroit carmakers.