The Animal and Plant Health Inspection Service of the U.S. Department of Agriculture has issued a movement permit to S. Claus to "allow reindeer to enter and exit the United States between the hours of 6 PM December 24, 2013 and 6 AM December 25, 2013, through or over any northern border port."
Since this is a government agency, things are not quite that simple:
As a condition of entry, the reindeer must be certified by Santa Claus as never having been fed anything other than hay, sugar plums, and gingerbread. The reindeer must also be individually identified with microchips or official eartag identification, and must respond to the names 'Dasher', 'Dancer', 'Prancer', 'Vixen', 'Comet', 'Cupid', 'Donner,' 'Blitzen' and 'Rudolph' when interacting with port personnel. No more than one reindeer in the group may be visibly affected by 'Rednose Syndrome', and upon entry, port personnel will visually inspect the reindeer to ensure they are healthy and fit for continued travel.
But APHIS waived the normally applicable disease testing requirements as well as the normal application fees and entry inspection/overtime costs.