Consumer and civil rights organisations around the world have asked the European Parliament to oppose clauses in the Anti-Counterfeiting Trade Agreement (Acta) that permit authorities to bar internet users from sharing files.
European negotiators are due to present their response to a US proposal on policing the internet for illegal file-sharing on 17 December.
"It is now time for the European Union to firmly oppose the dangerous measures secretly being negotiated, such as 'three strikes' schemes and content filtering on the internet," said La Quadrature du Net, one of the signatories to an open letter sent to the European Parliament.
The letter said it appeared that Acta went far beyond current EU law. It said a recent analysis by the European Commission of the Acta chapter on the internet confirmed that the current proposals "would profoundly restrict the fundamental rights and freedoms of European citizens, most notably the freedom of expression and communication privacy".
"These are very much at risk, since the current draft pushes for the implementation of three-strikes schemes and content filtering policies by seeking to impose civil and criminal liability on technical intermediaries such as internet service providers," the letter said.
"The text would also radically erode the exercise of interoperability that is essential for both consumer rights and competitiveness," it said.
The signatories also objected to the fact that European Parliamentarians had been denied access to the negotiating documents, but commercial US firms had had access to them under non-disclosure rules.
In April, the US trade department issued a summary of the Acta issues and said: "The intended focus is on counterfeiting and piracy activities that significantly affect commercial interests, rather than on the activities of ordinary citizens.
"Acta is not intended to interfere with a signatory's ability to respect its citizens' fundamental rights and civil liberties, and will be consistent with the WTO Agreement on Trade-Related Aspects of Intellectual Property Rights (TRIPS Agreement) and will respect the Declaration on TRIPS and public health," it said.
Acta is a secret multilateral trade agreement that has been negotiated for about 18 months. It is aimed at making it easier to fight counterfeiters of products from pharmaceuticals to software. It has been sponsored largely by film, video and music publishers.