The Advertising Standards Authority (ASA) has censured Plusnet for potentially misleading customers when promoting broadband packages.
The provider wrote on its website on January 2015 that some of its packages offered "totally unlimited" and "unlimited downloads - truly unlimited broadband with no usage limits. Browse and download around the clock".
However, a complainant took issue with Plusnet on the understanding that it imposed a traffic management policy.
The provider was therefore challenged to substantiate the claims and answer whether they could possibly be misleading.
Plusnet said that while it did not impose restrictions, exclusions or provider-imposed limitations on the line speeds of totally unlimited customers, it did utilise traffic prioritisation to make sure users with slower connections get a better user experience.
The provider also pointed out that traditional traffic management can slow down a user's connection speed during peak times and can be imposed as a punitive measure when a person has used up their allocated usage quota.
However, it stressed that traffic prioritisation is different as its purpose is to improve the service and it does not slow down a customer's connect speed or limit the bandwidth below the maximum capacity.
The ASA responded by saying CAP guidance makes it clear that unlimited claims are likely to be acceptable if provider-imposed limitations that affect the user's speed or service are moderate at best and clearly explained in the marketing communication.
However, it said the term "totally unlimited" is stronger and could make consumers believe that the service is free from any provider-imposed limitations. The ASA has therefore insisted that the ad must not appear again in its current form.
"We told Plusnet plc to describe their service as 'totally unlimited', only if there were no provider-imposed limitations to the service and to explain clearly any limitations they applied to their 'unlimited' service," it said.