The head of the government's religion office, Wang Zuo'an, says foreign forces have used religion to infiltrate China.
It follows a boom in followers to Christianity, many of whom worship in illegal 'house' churches to evade authorities.
In an old apartment block in Beijing, a covert gathering of Christians is taking place.
Every week they meet to read the Bible, pray and sing songs.
But what they're doing is Illegal, so they meet on Friday rather than Sunday, when the risk would be too high.
The apartment belongs to Pastor Xu Yonghai, who leads the group.
"I've been arrested 3 times, the first time in the 90s I was sent to a labour camp for 2 years. In 2003 I was sentenced to two years in prison. In 2014, 13 of us were arrested. Our church community has faced serious oppression, but we stay together."
Pastor Xu says he, like many others, found religion after the social and political upheaval of the Cultural Revolution in the 1960s and 70s.
"After the Cultural Revolution people realised they couldn't put faith in communism. They needed something else to believe in."
International Christian NGOs say there are up to 100 million Christians in China today, and they're being targeted by the government.
Bob Fu works for China Aid, a Christian NGO which monitors the treatment of China's Christian community from the United States.
"We definitely have been seeing a major deterioration and worsening. That has to do with the overall President Xi regime's hardening policy."
The Communist Party has just published an article banning its approximately 90 million members from believing in anything other than Marxist atheism.
Wang Zuo'an, director of China's State Administration for Religious Affairs, wrote that "foreign forces have used religion to infiltrate China."
Freedom of religion is technically protected in China but independent churches are outside the Party's control and seen, therefore, as a threat, says Bob Fu.
"To the Communist party in China, any social group or organisation perceived outside the total control and management of the Chinese Communist Party and its regime, is always regarded as a political threat."
The state only recognises two official churches: the Protestant 'Three-Self Patriotic Movement', based on the principles of "self-governance, self-support, and self-propagation", and its Catholic counterpart, the 'Chinese Patriotic Catholic Association.'
But Catholic clergy in China must swear allegiance to the Chinese Communist Party, not the Vatican.
Concealing his identity to avoid punishment for speaking out, this human rights lawyer says one of his clients was recently charged for 'disturbing public order' after holding an unsanctioned four-person Bible study at home.
"Previously people caught in home churches would be detained for 15 days at most. Now they're being charged and sentenced to three, four or five years in jail, even six and seven years."
Mr Wang says treatment of Christians varies throughout China, depending on local authorities.
But churches previously allowed to grow unhindered have faced, in recent years, intense scrutiny.
In May followers from a Christian church in China's southern Zhejiang province were detained for attempting to prevent local authorities from installing surveillance cameras in their building.
Churches around the country, most recently in the north-eastern Henan province, have been demolished for being "illegal" or "unsafe" structures.
"In Zhejiang province this year all the Churches received the directive to install face-recognition video cameras in every church to monitor church activities. And the church is asked to leave an office space for the party leader in the local government to monitor church offerings."
Churches around the country, most recently in the north-eastern Henan province, have been demolished for being "illegal" or "unsafe" structures.
Pastor Xu is aware of the risk, but says it's nothing compared to earlier decades and it will ultimately backfire.
"A lot of christians were arrested and sent to labour camps some were charged with crimes But in the 90s it grew the fastest. So the more they suppress us, the faster we'll grow."
If he's forced to face a fourth term in jail, he says it will be worth it.
