Germany's Roman Catholics are to be denied the right to Holy Communion or religious burial if they stop paying a special church tax.
A German bishops' decree which has just come into force says anyone failing to pay the tax - an extra 8% of their income tax bill - will no longer be considered a Catholic.
The bishops have been alarmed by the number of Catholics leaving the Church.
They say such a step should be seen as a serious act against the community.
All Germans who are officially registered as Catholics, Protestants or Jews pay a religious tax of 8-9% on their annual income tax bill. The levy was introduced in the 19th Century in compensation for the nationalisation of religious property.
"If your tax bill is for 10,000 euros, then 800 euros will go on top of that and your total tax combined will be 10,800 euros," Munich tax accountant Thomas Zitzelsberger told the BBC news website.
Catholics make up around 30% of Germany's population but the number of congregants leaving the church swelled to 181,000 in 2010, with the increase blamed on revelations of sexual abuse by German priests.
Alarmed by their declining congregations, the bishops were also pushed into action by a case involving a retired professor of church law, Hartmut Zapp, who announced in 2007 that he would no longer pay the tax but intended to remain within the Catholic faith.
The Freiburg University academic said he wanted to continue praying and receiving Holy Communion and a lengthy legal case between Prof Zapp and the church will reach the Leipzig Federal Administrative Court on Wednesday.
"This decree makes clear that one cannot partly leave the Church," Germany's bishops' conference said last week, in a decision endorsed by the Vatican.
Unless they pay the religious tax, Catholics will no longer be allowed receive sacraments, except before death, or work in the church and its schools or hospitals.
Without a "sign of repentance before death, a religious burial can be refused," the decree states. Opting out of the tax would also bar people from acting as godparents to Catholic children.
"This decree at this moment of time is really the wrong signal by the German bishops who know that the Catholic church is in a deep crisis," Christian Weisner from the grassroots Catholic campaign group We are Church told the BBC.
But a priest from Mannheim in south-western Germany, Father Lukas Glocker, said the tax was used to do essential good works.
"With kindergarten, with homes for elderly or unemployed, we've got really good things so I know we need the tax to help the German country to do good things."
While the decree severely limits active participation in the German Catholic Church, it does hold out some hope for anyone considering a return to the fold.
Until now, any German Catholic who stopped payment faced eventual excommunication. Although the measures laid out in the decree are similar to excommunication from the church, German observers say the word is carefully avoided in the decree.