As of right now, your Nintendo Network ID is locked down to the Wii U you created it in.
According to Nintendo’s Support Page, a user cannot log into his or her NNID from another console, at least for now:
A Nintendo Network Account can only be used on the console where it was created. In the future, you will be able to use your Nintendo Network Account with future Nintendo consoles and other devices, such as PC’s.
The Wii U can also support up to 12 unique IDs, but it begs the question, “what happens if your Wii U breaks?”
We’ve sent an email to Nintendo to find out if there’s a workaround in such a case.