Companies run a refreshed background check on you for transfers, promotions, or even department changes. They even run one on a current employee if they fall from grace with a manager looking for an excuse to fire you.
It doesn’t mean that they do this for a chicken plucker. Nor does it mean they actually take any action on the results. Please don’t try and tell me these places do not overlook some of their employees’ citizenship status.
They will do whatever it takes so that it will appear they are logically blameless. But that doesn’t mean they are acting legally.