The companies are very careful in the language and punishments. If a driver refuses a load because the trucks turn signals are out as an example, well the company will not come right out and say "You must take the load" but that driver will likely find himself sitting for possible days unpaid waiting for the next dispatch as punishment or they will be assigned the less profitable routes, etc

I know personally more than a few drivers that would pay out of their own pocket to buy parts to fix trucks themselves so they would not end up in this dispatch punishment.