In the U.S. protests , Web sites including Wikipedia went dark Jan. 18, and more than seven million people signed Google’s online petition opposing the Stop Online Piracy Act and the Protect Intellectual Property Act. Ultimately, even the bills’ sponsors in the U.S. Congress backed down under the onslaught of public criticism. 

The European activists are hoping to use similar pressure to stop the international Anti-Counterfeiting Trade Agreement, or ACTA, which is meant to clamp down on illegal commerce in copyrighted and trademarked goods. Opponents say that it will erode Internet freedom and stifle innovation. About 1.5 million people have signed a Web petition calling for the European Parliament to reject ACTA, which some say is merely SOPA and PIPA on an international level. Thousands of people have turned out for demonstrations across Europe, with more scheduled for next Saturday.

After more than three years of talks, which critics say were conducted without sufficient public input , the United States signed on to ACTA last October in Tokyo, along with Australia, Canada, Japan, Morocco, New Zealand and South Korea. (The agreement is to come into force when six of those countries have ratified it.)

But the issue moved into the mainstream in Europe after the European Union and representatives of 22 of 27 E.U. members — all except Cyprus, Estonia, Germany, the Netherlands and Slovakia — signed Jan. 26.

On the same day, Kader Arif, a French Socialist member of the European Parliament, quit as the body’s special rapporteur for ACTA. He said the European Parliament and civil society organizations had been excluded from the negotiations, and he denounced the entire process as a “masquerade.” The issue, which had gotten little traction in the news media previously, began to move into the headlines, with calls for national legislatures and the European Parliament to reject the treaty.

The pressure on politicians has been unrelenting. Helena Drnovsek-Zorko, the Slovenian diplomat who signed the treaty on behalf of her country, has publicly disowned it and called for her fellow citizens to demonstrate against it. Ms. Drnovsek-Zorko said that she had signed “out of civic carelessness” and that it was her conviction that ACTA “limits and withholds the freedom of engagement on the largest and most significant network in human history.”

Poland, the home of some of the most vocal protests to date, “suspended” ratification, said the Polish prime minister, Donald Tusk, after politicians wearing the Guy Fawkes masks favored by the online vigilante group Anonymous protested in the Polish Parliament.

ACTA seeks to provide a common framework of civil and criminal procedures to stop illegal trade in goods and properties — like Louis Vuitton bags, Hollywood films and recorded music — providing holders of intellectual property rights with the means to work through the courts outside their national borders to shut down counterfeiters and pirates. And though two piracy heavyweights, Russia and China, have not signed, ACTA’s drafters say they hope those countries will come to see the benefits of joining.

Mr. Arif, the opponent to the measure in the European Parliament, said that ACTA was “wrong in both form and substance.”

He said European officials, who began negotiating the agreement in 2007, kept legislators in the dark for years and ignored their concerns, finally presenting them with a finished deal for ratification with no option of modifying it.

“Voilà, that’s the masquerade that I denounce,” he said. Mr. Arif said a number of issues in the agreement troubled him, particularly a provision that could make Internet service providers liable for copyright infringement by users, something that would be in conflict with existing E.U. law.

Another provision, he said, appeared to roll back protections for generic drugs by lumping them in with counterfeit drugs.

Further, he said, the law leaves to the discretion of each country the definition of what constitutes a “commercial” level of piracy, so some countries might choose to search travelers’ laptop computers and digital music players in search of illegal downloads. ACTA supporters reject the criticism and say action is essential when legitimate owners of intellectual property are losing tens of billions of dollars annually to counterfeiting and illegal sharing. They accuse some opponents of deliberately exaggerating ACTA’s provisions to fan fears.

“ACTA is about enforcing existing intellectual property rights and about acting against large-scale infringements often pursued by criminal organizations, and not about pursuing individual citizens,” said John Clancy, the E.U. trade spokesman.