Shortly after its European release in 2013, Wii Karaoke U sparked controversy in the region due to the game allowing players to download and perform songs with explicit lyrics despite the game's family-friendly presentation and PEGI 3 rating. This is in stark contrast to similar karaoke games that include clean versions of explicit songs. The only indication of this leniency is on the loading screen, which includes the text "MUSIC DOWNLOADS NOT RATED BY PEGI." The fact that this occurred shortly after Nintendo removed online connectivity from Swapnote due to child predation concerns attracted further criticism.

Upon being contacted by multiple journalists about the game's content, Nintendo (who did not develop the game, but nonetheless authorized its publication) responded by stating that they would add a mature content warning to its Nintendo eShop page. They also stated that they chose not to restrict the kinds of songs available in order to "appeal to all music tastes," pointing out that enabling parental controls prevents child players from downloading tracks without a PIN code.