The European proposal, offered for debate at a December meeting of a U.N. agency called the International Telecommunication Union, would amend an existing telecommunications treaty by imposing heavy costs on popular Web sites and their network providers for the privilege of serving non-U.S. users, according to newly leaked documents.

The documents (No. 1 No. 2) punctuate warnings that the Obama administration and Republican members of Congress raised last week about how secret negotiations at the ITU over an international communications treaty could result in a radical re-engineering of the Internet ecosystem and allow governments to monitor or restrict their citizens’ online activities.

“It’s extremely worrisome,” Sally Shipman Wentworth, senior manager for public policy at the Internet Society, says about the proposed Internet taxes. “It could create an enormous amount of legal uncertainty and commercial uncertainty.”