Census workers can enter your apartment in your absence | The Barr Code

What many Americans don't realize, is that census workers — from the head of the Bureau and the Secretary of Commerce (its parent agency) down to the lowliest and newest Census employee — are empowered under federal law to actually demandaccess to any apartment or any other type of home or room that is rented out, in order to count persons in the abode and for "the collection of statistics."  If the landlord of such apartment or other  leased premises refuses to grant the government worker access to your living quarters, whether you are present or not, the landlord can be fined $500.00.

http://blogs.ajc.com/bob-barr-blog/2010/05/26/census-workers-can-enter-your-apartment-in-your-absence/