The description of an "underground church" reflects language that was made popular during the Cold War, when these churches came about. Underground churches are also sometimes referred to as "Vatican loyalists" because they have attempted to remain loyal to the Pope and the Holy See. There is no established organization structure of underground churches, though they tend to be clustered around a number of Vatican-ordained bishops. However, underground churches would in 1989 form the Bishops Conference of Mainland China as separate from the state-sanctioned :zh:中國天主教主教團|Bishops Conference of Catholic Church in China, which was established in 1980. Chinese Catholics associated with underground churches are often seen in contrast with the Chinese Catholics associated with the Chinese Patriotic Catholic Association, often termed "open churches", which are officially independent of the Holy See. Protestant churches in China which have not jointed the state-sanctioned Protestant church, the Three-Self Patriotic Movement, are generally termed house churches rather than underground churches.
Legality
Underground churches in China are considered illegal, although smaller groups of fewer than 5 members are sometimes tolerated by the government. Chinese Patriotic Catholic Association and :zh:中國天主教主教團|Bishops Conference of Catholic Church in China are often used by the government to oppress underground churches throughout China. The underground churches used to be supported by the Roman Catholic Diocese of Hong Kong during the term of Joseph Zen. It is not unusual that Chinese Catholics attending underground churches get arrested, detained without trial, even tortured. While there are churches for expatriates and expat Christians staying in China are allowed to have their own churches which are not interfered by the government, foreigners, including those of Chinese heritage, found involved with underground churches will be arrested and deported. For security reason, most overseas Chinese churches, even the Chinese Regional Bishops' Conference, the only Chinese Bishops' Conference recognised by the Holy See which is nowadays based in Taiwan, refuse to support the underground churches in China.
