An amendment proposed to the Digital Economy Bill would force internet service providers (ISPs) to block pornographic websites if they fail to verify the age of a visitor.
The bill, which is now in the final stage of consideration in Parliament, originally set out to impose age restrictions on all pornographic websites, forcing users to state how old they were before accessing material.
The bill states that "a person must not make pornographic material available on the internet on a commercial basis to persons in the UK, except in a way that secures that, at any given time, the material is not normally accessible by persons under the age of 18."
Now a group of MPs have put forward a change that would block sites that failed to assess the age of their visitors, determined by a government-appointed 'age verification regulator'.
The government believes the new powers will help protect children from accessing inappropriate material on the internet.
However, Open Rights Group (ORG), a digital free speech organisation, argued the bill is an infringement on human rights, and a complete block on content should only be reserved for those sites showing illegal material.
"Perhaps these MPs have realised that plans to make all adult websites apply age verification are unworkable as foreign porn sites may simply not comply," said Jim Killock, executive director of ORG.
"While child protection is important, this proposal is disproportionate. Censorship of this kind should be reserved for illegal and harmful content," added Killock.
Under the new bill proposed by Conservative MP Claire Perry, the regulator can fine any ISP that fails to block websites violating the new terms.
The bill will also target suppliers of content and 'ancillary services', which include card payment providers and advertising. The hope is that porn sites failing to comply with the new rules will not only have their content blocked, but will struggle to make money from UK customers.
However ORG argues that "ancillary services could include website hosts, search engines, DNS services, web designers... this needs restriction just for the sake of some basic legal certainty".
"We are talking about potentially thousands of websites with legal material being censored, something that is unprecedented in the developed world," said Killock.
The bill, which is set to come into law in 2017, will address a swathe of issues related to electronic communications, including broadband obligations, intellectual property and fraud against the public sector.
