The registrar also argued against a second decision that said domain names are not protected by the First Amendment.
The appeal, filed by New York City-based Name.Space (formerly PG Media), seeks to reinstate an antitrust lawsuit the company filed against NSI in 1997. U.S. District Judge Robert Patterson dismissed the lawsuit in March, holding that a cooperative agreement NSI signed with the federal government immunized it from antitrust claims.
Name.Space, which sells domain names with more than 500 different extensions, or top-level domains, claims that NSI's refusal to add the addresses to its database is a violation of antitrust laws. The suit also claims that the refusal violates free speech guarantees because the addresses carry expressive value.
NSI and the National Science Foundation, which also was named in the suit, claim that under the so-called federal instrumentality doctrine, neither federal agencies nor their contractors may be sued for antitrust violations. The defendants also argue that domain names are like telephone numbers and do not constitute speech for purposes of the Constitution.
Name.Space's brief, filed this week with the U.S. Court of Appeals for the Second Circuit, argues that private companies can be immunized from antitrust lawsuits only through an explicit act of Congress.
"In the absence of express congressional immunity, repeals of the antitrust laws by implication are 'strongly disfavored,'" the appeal argues.
Representatives from Network Solutions were not immediately available to comment.
The appeal also mentioned a decision issued in May by an appeals court in Washington, D.C., that cast doubt on NSI's immunization arguments.
"It is not obvious to us...that a private contractor automatically shares the federal agency's immunity simply because the contractor's allegedly anticompetitive conduct occurred--as NSI puts it and some courts suggest--'pursuant' to a government contract," the panel wrote.
NSI has 30 days to respond to the appeal. Oral arguments are expected in the fall.