The Advertising Standards Authority has upheld a complaint against Labour's "John and John" campaign ads and has ruled they carry misleading information.
The ads, which present conflicting statements made by National Party leader John Key, are on radio, television and the YouTube website.
The authority can deal only with the ones on YouTube - which are identical to the others - because radio and TV come under the Broadcasting Act, and the ads are classed as election programmes.
The authority has upheld a complaint by S Davies-Colley who argued the comment "he (Mr Key) wants to cut KiwiSaver in half" was misleading.
The authority's complaints board decided by majority it was misleading because only part of National's KiwiSaver policy cuts contributions in half and savers have other options.
The Labour Party argued the opposite and filed pages of information about KiwiSaver.
Authority's executive director Hilary Souter told NZPA it could ask Labour to withdraw the ad from YouTube but had no statutory authority to order it to be removed.
"We have a really good level of compliance...in fact we've had previous compliance from Labour," she said.
"We've no reason to believe they won't comply."