Add enough money to your North America Wii U eShop account by July 28 and receive $5 or $10 eShop credit.
Monday Nintendo distributed a Wii U promotional newsletter that advertised up to a $10 eShop credit for Wii U owners that add enough funds to their Wii U eShop account before the deadline.
Details of the promotion are explained on the Club Nintendo website. Wii U owners that add between $50.00 and $99.99 in funds before the deadline will receive a promotional code via email worth $5.00 eShop credit. Those who add $100.00 or more will receive a $10 credit. This offer is valid in the United States and Canada and, according to the fine print, the code can only be redeemed on Wii U.
This promotion is valid now through July 28 at 11:59 p.m. PST.