Negotiations over a controversial anti-piracy agreement have been described as a "masquerade" by a key Euro MP.
Kader Arif, the European Parliament's rapporteur for the Anti-Counterfeiting Trade Agreement (Acta), resigned from the post over the issue on Friday.
He said he had witnessed "never-before-seen manoeuvres" by officials preparing the treaty.
On Thursday, 22 EU member states including the UK signed the agreement.
The treaty still needs to be ratified by the European Parliament before it can be enacted. A debate is scheduled to take place in June.
Mr Arif criticised the efforts to push forward with the measures ahead of those discussions taking place.
"I condemn the whole process which led to the signature of this agreement: no consultation of the civil society, lack of transparency since the beginning of negotiations, repeated delays of the signature of the text without any explanation given, reject of Parliament's recommendations as given in several resolutions of our assembly."
Mr Arif's decision to stand down as rapporteur - he remains an MEP - follows protests by campaigners in Poland. Thousands of demonstrators took to the streets after the agreement was signed.
Crowds of mostly young people held banners with slogans such as "no to censorship" and "a free internet".
Earlier in the week, hackers attacked several Polish government websites, including that of Prime Minister Donald Tusk.
The country's Foreign Minister Radek Sikorski defended the plans, telling local television: "We believe that theft on a massive scale of intellectual property is not a good thing."
Campaigners' concerns have been buoyed by Mr Arif's strongly-worded statement released on Friday.
"This agreement can have major consequences on citizens' lives," he wrote.
"However, everything is made to prevent the European Parliament from having its say in this matter. I want to send a strong signal and alert the public opinion about this unacceptable situation. I will not take part in this masquerade."
The treaty has caused controversy since an early discussion paper was published by Wikileaks in 2008 - two years after negotiations first began. The details were subsequently confirmed in 2010.
If ratified, it proposes to improve "the enforcement of intellectual property rights" in participating countries.
It suggests setting international standards over how copyright infringements are dealt with, with preventative measures including possible imprisonment and fines.
The UK's Intellectual Property Office has backed the measures, describing piracy as a "major global issue".
"Yesterday's signing of Acta is important for the UK as it will set an international standard for tackling large-scale infringements of IPR, through the creation of common enforcement standards and more effective international cooperation. Importantly, it aims to improve the enforcement of existing IPR laws, not create new ones," it said.
Darrell Issa, a US congressman and vocal critic of the stalled Stop Online Piracy Act (Sopa), voiced his concerns about Acta at the World Economics Forum in Davos.
"As a member of Congress, it's more dangerous than Sopa," he said.
"It's not coming to me for a vote. It purports that it does not change existing laws. But once implemented, it creates a whole new enforcement system and will virtually tie the hands of Congress to undo it."
In addition to internet-based measures, the agreement also seeks to curb trade of counterfeited physical goods.
Past drafts of the treaty suggested that internet service providers would have to give up data about users accused of copyright infringement and might have to cut them off - although this segment of the agreement has since been removed.
Outside of the EU, the treaty has also been signed by the US, Australia, Canada, Japan, Morocco, New Zealand, Singapore and South Korea.
In response to Mr Arif's resignation, a spokesman for the European Commission told the BBC: "Mr Arif and other members of the European Parliament's [Committee on International Trade] have had access to successive versions of the Acta text. The full text has been fully public since April 2010. It was made available in the first place because the European Commission convinced the other countries to publish this text.
"There have been four stakeholder conferences since 2008, and at least three speeches in the European Parliament on Acta. And now there will be a full debate. This is exactly what the normal process is.
"But most importantly Acta does not change any EU laws, it simply levels the playing field so that other countries match our standards. There is no threat to internet freedom or privacy. Everything you can do legally today in the EU, you would be legally able to do if Acta is ratified."