The Advertising Standards Authority (ASA) has banned an EE advert that claimed the company provides the "most reliable" broadband.
A complaint was made about the commercial by BT, which said such an assertion could not be substantiated and was misleading.
While EE argued the claim was based on findings released in a recent Ofcom report, the ASA supported BT's argument that this was not clear enough for the claim "most reliable" broadband to be made accurately.
The organisation has ruled the advert must not appear in its current form again. EE is not the only company to have a promotion banned on these grounds, as BT itself had an advert that made a similar claim withdrawn in 2012.
Earlier this month, the ASA ordered BT to ensure the speed checker feature on the company's website provides more accurate information.
A complaint had been filed about the service after it said download speeds of between 23 Mbps and 33 Mbps were available in a particular location when this was not the case.