Angry animal rights activists are planning large-scale protests this weekend after four of their colleagues were sentenced to federal prison for their campaign of harassment against a British-based research company with offices in New Jersey that performs tests on animals. Four activists from the Stop Huntingdon Animal Cruelty, SHAC, were sentenced to three to six years in prison following hearings in federal court in Trenton, New Jersey, for violations of the Animal Enterprise Act. Two more members are scheduled to be sentenced to lesser terms next week. The weekend-long protests in Princeton, New Jersey, have been planned since August when Hugs for Puppies founder David Lambon sent out an email, urging protesters to show up and "show the world that the campaign against HLS is still here, still strong and still holding the business world accountable for supporting Huntingdon Life Services." THE BLOTTER RECOMMENDS FBI: Cyber Blackmail by Animal Rights Hackers ‘Terror’ Group Web Site a Puzzle for Feds Click Here for More of the Brian Ross Page According to a law enforcement bulletin obtained by ABC News and circulated to businesses that may be affected, including chemical and biotech companies in the northern New Jersey-Pennsylvania area, while there is no confirmed evidence of plans of violence, "direct criminal action" has been a hallmark of SHAC and has occurred in the past. Law enforcement officials in Philadelphia say they are also on alert for protests scheduled there on Sunday afternoon in solidarity with SHAC. In the past, SHAC activists have clogged phone lines to HLS and companies that conducted business with it, harassed employees at home and posted home addresses and names of family member online.