[1] Deuteronomy 15-17
Echos of this are found in Revelations, where all are required to have a number for buying and selling.
A census was used to assess a nation's fitness for battle and to set a taxing expectation.
Revelation is discussing the state of affairs under the rule of Nero (the man whose name has the number 666, or 616 depending on the source of your translation). Presumably, it became difficult to do business if you were not known to be loyal to the emperor.
(Side note: You are probably meaning to reference 2 Samuel 24 / 1 Chron 21 when you claim that unsanctioned censuses were prohibited, though that's never actually stated. Just, everybody in the story knows that what they're doing is wrong. But plenty of commentary has been written about why David's census was problematic.)
I think this would make an interesting dystopian novel.