Nintendo has scheduled maintenance for the Nintendo Network starting Monday, January 11, 2016. Though not many details have been given so far, we do know that certain network services such as online play and rankings will be affected on both Wii U and Nintendo 3DS systems.
The maintenance is set for January 11 at 8pm EDT/5pm PDT to January 12 at 6am EDT/3am PDT. Be mindful of this time frame to avoid any inconveniences.
As always, gaming is meant to be fun, so keep gaming!!