Plusnet's recent television advert for half-price broadband has been banned by the Advertising Standards Authority (ASA).
The regulator ruled that the broadband provider failed to make the terms of its offer sufficiently clear to consumers.
According to the ASA, the advert did not clearly explain that customers were required to take out line rental in order to qualify for the half-price broadband offer.
It said the wording of the advert was likely to be misinterpreted by viewers, with Plusnet failing to make clear that line rental - advertised at £13.99 per month - was mandatory.
"We considered that was a significant condition of the promotion that was not made sufficiently clear," the ASA stated.
"The word 'with' was not sufficient to counteract the overall impression of the ad, which was that all broadband was half price. On balance, we therefore concluded that the ad was misleading."
The ASA banned Plusnet's advert and told the service provider to ensure that any "significant conditions" of promotions are made clear in future.