USTR released 36 pages about the Anti-Counterfeiting Trade Agreement (ACTA) on April 30, but there are still more than 1,000 pages on the antipiracy agreement being withheld, digital rights groups Public Knowledge and the Electronic Frontier Foundation (EFF) said. ACTA, being negotiated among the U.S. and several other countries in secret, could require countries agreeing to the pact to enforce each other's copyright laws, according to released in early April.

"We are very disappointed with the USTR's decision to continue to withhold these documents," EFF senior counsel David Sobel said in a statement. "The president promised an open and transparent administration. But in this case and others we are litigating at EFF, we've found that the [president's] new guidelines liberalizing implementation of the Freedom of Information Act haven't changed a thing."

ACTA could have a huge impact on U.S. residents' privacy and on innovative new technologies, the groups said.

One of the documents released suggests that treaty negotiators are looking at regulating the Internet, the groups said. The document lists as a copyright enforcement challenge "the speed and ease of digital reproductions" and "the growing importance of the Internet as a means of distribution."

The two groups filed a lawsuit against USTR in September, complaining that the agency had largely ignored their Freedom of Information Act request to disclose details of the trade pact, which has been negotiated among the U.S., Japan, the European Union and other countries since 2006. USTR initially released 159 pages about ACTA but denied access to 1,300 other pages, saying that information was withheld for reasons of national security or to protect the USTR's deliberative process.