Countdown has been ordered to withdraw advertisements for a "one-day sale'' that ran online for 21 hours over two days.
The television ad included a voiceover stating the sale was on "only tomorrow and only at Countdown''.
However, fine print at the bottom of the screen clarified the sale prices were valid "in-store on Wednesday 18 September 2013 only or online from 4pm Tuesday 17 - 1pm Wednesday 18 September 2013''.
A complaint to the Advertising Standards Authority from T Orwin said people would expect to be able to purchase the goods on the Wednesday referred to in the ad, rather than the 21-hour period specified in the fine print.
The response from Progressive Enterprises said the promotion was valid all day Wednesday in-store, but differed for online because 1pm was the cut off for same-day delivery.