Virgin Media has refused to sign up to the Open Internet Code of Practice, complaining the guidelines are open to "misinterpretation and potential exploitation", while Everything Everywhere and Vodafone have also refused to sign, the latter dubbing the code "impractical", according to the BBC.
This code extends an earlier traffic management agreement that the three firms did sign up to. It adds three new commitments:
The three ISPs seem particularly vexed about the second and third commitments.
"These principles remain open to misinterpretation and potential exploitation so, while we welcome efforts to reach a broad consensus to address future potential issues, we will be seeking greater clarity before we consider signing," Virgin said in a statement.
A Vodafone spokesperson told Computing: "Essentially, it boils down to the way they've worded the final code.
"We are not against the principles behind the code – having signed up to last year's Transparency Code – but are concerned that the language would have resulted in us having to give a very confusing message to customers – that their phones do not offer ‘internet access' when they do offer access to the internet."
The spokesperson's comments were backed up by a media statement from Vodafone, which explained how many of its customer plans "offer internet access to smartphone and dongle users", but that under the code, Vodafone would be "unable to use the phrase ‘internet access' to describe many of the services enjoyed by customers".
Everything Everywhere said in a statement: "As the market and content delivery models are still evolving, [the Orange and T-Mobile partnership believes] it is too early to know how a code of this type will affect customers' internet experience."
Everything Everywhere stated it also supports open internet and transparency as a "principle".
Matthew Howett, lead analyst of regulatory telecoms at analysis firm Ovum, said he understood the three companies' misgivings about the code, saying that the issue of how "full internet access" is marketed is "less clear at this stage".
"With no commonly used term to describe internet access with restrictions – which is a fairly common practice – some more clarity form the Broadband Stakeholders Group would be useful," said Howett.
Pamela Learmonth, chief executive of the Broadband Stakeholder Group, explained: "All of the signatories to this code offer full, open internet access across all of their current products.
"The code also confirms the ability of ISPs to explore managed services; a market development that Ofcom has committed to monitor."
Ten ISPs, including Three, Plusnet, BskyB and Tesco Mobile have all signed up so far. Virgin, Vodafone and Everything Everywhere have all stated they support the principle of an open internet, but have issues with certain parts of the code.