In 1971, he retired and applied for permission to emigrate to Israel. Denied on grounds of knowing state secrets, he soon became a refusenik. Gradually he became more active in politics, and was a member of the Moscow Helsinki Group beginning in 1977. Later he became deputy chairman and the last active free member, writing hundreds of the group's documents. He also participated in a Refusenik scientific seminar. He was permanently under surveillance by the KGB, who also bugged his telephone and searched his home.