Pokemon X/Y's online will also be down for an extended period of time.
http://www.nintendoworldreport.com/news/36802/maintenance-for-nintendo-network-scheduled-next-week
Various activities surrounding the Nintendo Network will be stopped temporarily at some point this week.
Beginning Monday, March 10 at 5 p.m. Pacific Time/Tuesday, March 11 01:00 CET, all the online services for Pokemon X and Y will be unavailable for a period of 14 hours. This includes online play, rankings, watching match replays and everything else that relates to this game. It will back up and running on Tuesday, March 11 at 7 a.m. Pacific/15:00 CET.
On Thursday however, both versions of the Nintendo eShop on the Wii U and Nintendo 3DS will be taken offline for four hours. This will start at Thursday March 13 at 1 p.m. Pacific Time/21:00 CET and ends at Thursday, March 13 at 5 p.m. Pacific Time/Friday, March 14 at 01:00 CET.
A reasoning for the downtime was not given by Nintendo, though we will keep you up to date if anything related to these services changes.