From the Holocaust Museum....
Even before 1933, Jehovah's Witnesses were targets of prejudice. Mainstream Lutheran and Catholic churches deemed them heretics. Moreover, citizens often found the Witnesses' missionary work--knocking on doors and preaching--to be invasive. Individual German states had long sought to curb the missionary work through strict enforcement of statutes on illegal solicitation. At various times, individual jurisdictions actually banned Witness religious literature, including the booklets The Watchtower and The Golden Age. During the Weimar period, however, the German courts often ruled in favor of the religious minority.
Before the Nazis came to power, individual groups of local Nazis (party functionaries or SA men), acting outside the law, broke up Bible study meetings and assaulted individual Witnesses.
From the Wikipedia:
Throughout the history of Jehovah's Witnesses, their beliefs, doctrines and practices have engendered controversy and opposition from the local governments, communities, or religious groups. Persecution has been a recurrent experience of the Jehovah's Witnesses since its foundation. Ken Jubber writes that "Viewed globally, this persecution has been so persistent and of such an intensity that it would not be inaccurate to regard Jehovah's witnesses as the most persecuted religion of the twentieth century". Many Christian denominations consider their interpretation and doctrines to be heresy. Thus some religious leaders have accused Jehovah's Witnesses of being a cult. According to the eminent jurist Archibald Cox, in the United States, the Witnesses were "the principal victims of religious persecution... in the twentieth century... Although founded earlier, they began to attract attention and provoke repression in the 1930s, when their proselytizing and numbers rapidly increased." 
Political and religious animosity against them has at times led to mob action and government oppression, in countries such as Cuba, the United States, Canada and Nazi Germany. The religion's doctrine of political neutrality has led to the jailing of Witnesses who refused conscription (for example in Britain during World War II and afterwards during the period of compulsory national service). During the world wars, Jehovah's Witnesses were also targeted in the United States, Canada and many other countries because they refused to serve in the military or help with war efforts. In Canada, Jehovah's Witnesses were interned in camps along with political dissidents and people of Japanese and Chinese descent. Activities of Jehovah's Witnesses have previously been banned in the Soviet Union and in Spain, partly due to Jehovah's Witnesses refusal to perform military service. Their religious activities are currently illegal or restricted in some countries, for example in China, Vietnam, and many Islamic states.
There has been opposition expressed by locals in some communities to the building of facilities such as Kingdom Halls or the holding of large conventions. This sort of opposition has derived from various motives, such as opposition to the religion, or civil concerns such as traffic congestion and noise.[citations needed]