The right-wing think tank Heritage Foundation has joined the growing roster of opponents to a controversial anti-piracy proposal pending in Congress.

The organization warned this week that passage of the Stop Online Piracy Act (HR 3261) could harm online security, while also undermining free speech. “While the legislation’s goal -- the protection of property -- is a proper one, there are alternative approaches,” Heritage Foundation Senior Research Fellow James Gattuso says in a new report.

The Hollywood-backed bill provides for court orders banning ad networks and payment processors from doing business with “rogue” sites -- defined as sites dedicated to infringement. The proposal also provides for court orders banning search engines from returning certain results, and orders banning Internet service providers from putting traffic through to certain URLs.

The Stop Online Piracy Act was introduced in October by Reps. Lamar Smith (R-Texas), John Conyers (D-Mich.), Bob Goodlatte (R-Va.) and Howard Berman (D-Calif.). A companion measure, the Protect IP Act, is pending in the Senate.

The entertainment industry says the law is needed to stem infringement, particularly by companies that operate outside the U.S.

Web companies, as well as Internet engineers, law professors and digital rights advocates, oppose the legislation. Critics point out that even if ISPs filtered out domains, users could still reach the sites by typing in the numeric IP addresses. Users also could access IP addresses through servers located outside the U.S.

One key concern flagged by the Heritage Foundation (as well as Internet experts) stems from a fear that those foreign servers might not be secure, which could result in threats to U.S. networks. The Heritage Foundation also notes that the bill could thwart the Domain Name System Security Extensions -- an effort to improve security by making it harder to spoof sites. That concern was also articulated last week by Stewart Baker, former Department of Homeland Security Assistant Secretary.

The Heritage Foundation also takes issue with the prospect of court orders banning search engines from returning results. That provision “undercuts the role of search firms as trusted intermediaries in conveying information to users,” Gattuso writes.

“There has never been a government mandate that information be withheld from search results. Imposing such a mandate would represent the first step down a classic slippery slope of government interference that has no clear stopping point,” he adds.

The House Judiciary Committee considered the bill last week and will resume the markup process next year.