BPI, the organisation that represents music publishers, appears to have drafted the controversial Amendment 120a to the Digital Economy Bill put forward by Conservative and Liberal Democrat party lords.
The Open Rights Group, an organisation that opposes the bill, has published a document that purports to be the BPI's alternative to Clause 17, which deals with the prevention of illegal online file-sharing.
Shadow Digital Britain minister Jeremy Hunt told Computer Weekly that the amendment "needed more work" to stop it from producing "unintended consequences".
He said the Tories would continue to support the amendment, which is opposed by the government, because it would help to make the internet a viable marketplace.
Jim Killock, executive director of the Open Rights Group, said it was "totally irresponsible" for parliamentarians to include a major proposal from one part of industry in a bill without consultation.
"This proposal, drafted by the BPI, could produce backdoor web censorship and unjustified blocks on websites," he said. "That is what happens when only one side of a problem gets to influence the debate: and that is why we also have disconnection proposed as a punishment."
Killock said disconnection of families, advocated by the BPI, would damage innocent people's education, businesses and work, while giving extreme protections for copyright holders.
"Something very fundamental has gone wrong in this debate. We have a bill which is a complete mess, and large parts of it should be scrapped right now."
Both Clause 17 and Amendment 120a were condemned by the internet community and human rights activists. The CEOs of Google, BT, eBay and other leading internet companies and telecommunications operators have warned that the proposals would have a chilling effect on free speech.
They also said the measure would harm the operation of the internet in the UK and elsewhere, without stopping illegal file-sharing. As such, they were contrary to the aims of the bill, one of which is to maximise access to and use of the internet via high speed broadband.
BPI was unavailable for comment.