Which credit union? All the ones I've encountered incorrectly state that they require Social Security Numbers by law. The law only requires that they have a n

Which credit union? All the ones I've encountered incorrectly state that they require Social Security Numbers by law. The law only requires that they have a numerical identifier, so a state ID/license should work as it apparently did in your case. Edit: I guess the downvotes are for assuming everyone's in the U.S., sorry!