Nintendo has announced on their
Current Network Status page that
Pokémon X and Y will undergo Extended Maintenance on Monday, January 27th, 2014 at 4:00 PM Pacific Time until 10:00 PM. Online Play, Rankings and other features that require the Nintendo Network will be unavailable for players of
Pokémon X and Y.
Source:
http://www.nintendo.com/consumer/network/en_na/network_status.jsp