“This is a remarkable development that was virtually unthinkable even a year ago,” University of Ottawa law professor Michael Geist wrote on his blog, cheering the decision.

Backers of the Anti-Counterfeiting Trade Agreement, including the United States, Canada and Japan, said it would curb counterfeiting and illegal downloads and streaming of movies and music, creating a common international standard for policing piracy. Many countries have already signed ACTA. European associations tied to publishing, television and other creative industries hailed joining them as a way to protect their members' work.

But a range of organizations — from Internet freedom groups to aid agencies — argued that ACTA would have nasty side effects. Free speech groups complained that the pact could infringe on privacy and push Internet providers to police what people share online with few safeguards for their rights, drawing little distinction between people who use pirated files for their own use and those who profited from them.