I have seen this recently at Hilton's along the West Coast. Vancouver Hilton Metro is trying to enforce it..... but its not going over very well there. Last time I stayed there, I was told this and when I told them I would go elsewhere they removed it from the registration sheet. Same at the Oakland Hilton and the Claremont in Oakland.
Generally speaking the market is too soft for them to enforce such a silly rule and the clerk is stuck, they dont want to lose a reservation.
I should note that none of the above hotels had a method to alert me to this when I made my reservations.
------------------
AA member since 1981.