or imprisoned, and harassment of unregistered bishops and priests was common. There were reports of Catholic bishops and priests being forced by authorities to attend the ordination ceremonies for bishops who had not gained Vatican approval. Chinese authorities also had reportedly pressured Catholics to break communion with the Vatican by requiring them to renounce an essential belief in Catholicism, the primacy of the Roman Pontiff. In other instances, however, authorities permitted Vatican-loyal churches to carry out operations under strict surveillance. While Article 36 of China's Constitution provides for "freedom of religious belief" and non-discrimination on religious bases, it also states that "[n]o one shall use religion to engage in activities that disrupt public order, impair the health of citizens or interfere with the state's education system" and "[r]eligious groups and religious affairs shall not be subject to control by foreign forces." A major impediment to the re-establishment of relations between the Vatican and Beijing was the issue of who appoints the bishops. As a matter of maintaining autonomy and rejecting foreign intervention, the official church had no official contact with the Vatican and did not recognize its authority. In later years, however, the CPA allowed for unofficial Vatican approval of ordinations. Although the CPA continued to carry out some ordinations opposed by the Holy See, the majority of CPA bishops became recognized by both authorities. In a further sign of rapprochement between the Vatican and Beijing, Pope Benedict XVI invited four Chinese bishops, including two government recognized bishops, one underground bishop, and one underground bishop recently emerged into the registered church, to the October 2005 Synod on the Eucharist. On 27 May 2007, Pope Benedict XVI wrote a letter to Chinese Catholics "to offer some guidelines concerning the life of the Church and the task of evangelization in China". In this letter (section 9), Pope Benedict acknowledges tensions: Underground bishop Joseph Wei Jingyi of Qiqihar released a two-page pastoral letter in July 2007, asking his congregation to study and act on the letter of Pope Benedict XVI and naming the letter a "new milestone in the development of the Chinese Church." In September 2007, a coadjutor bishop for the Guiyang Diocese was jointly appointed by the Vatican and the Chinese official Catholic church. Demographics The number of Catholics is hard to estimate because of the large number of Christians who do not affiliate with either of the two state-approved denominations.