Switching jobs would incur a slight penalty of 1) removing chip, b) re-programming chip, c) leaving chip. I think this is something a lot of people would like to avoid.
My guess is that there would be no need to remove or reprogram. I assume the chip simply presents a unique identifier and nothing more. The old company could just remove access based on the identifier and in a similar way, the new company could grant access using the existing chip.