The six members of Stop Huntingdon Animal Cruelty were convicted in 2006 of using their Web site to incite threats and vandalism against employees of Huntingdon Life Science in Franklin Township, Somerset County, N.J.
The group posted home addresses and other information about the workers on the site.
Each activist was sentenced to six years in prison. Three remain in federal custody.
The 3rd U.S. Circuit Court of Appeals ruled there was enough evidence to convict them of violating the Animal Enterprise Terrorism Act.
The trial was believed to be the first to use the statute, which was enacted in 1992.