Nintendo has announced on their Current Network Status page that Pokémon X and Y will undergo Extended Maintenance from Monday, February 3rd, 2014 at 4:00 PM until Tuesday, February 4th, 2014 12:00 AM Pacific Time. Online Play, Rankings and other features that require the Nintendo Network will be unavailable for players of Pokémon X and Y. The Pokémon X and Y Game Sync duration will be changed to 3 hours after this maintenance window.

Source: http://www.nintendo.com/consumer/network/en_na/network_status.jsp