Priests in around 100 Catholic churches in Germany are offering blessings to same-sex couples from Monday.
The Love Wins movement emerged after the Catholic Church said in March that God “cannot bless sin”.
“Couples who take part should receive the blessing that God wants to give them – without any secrecy,” the group wrote earlier.
Pope Francis has previously said he believes same-sex couples show be allowed to have “civil unions”.
Last year, he told a documentary that these couples “have a right to be in a family”.
However, he has also approved the Congregation for the Doctrine of the Faith’s stance that the Catholic Church does not have the power to bless same-sex unions.
In the Catholic Church, a blessing is given by a priest or other minister in the name of the Church.
The Vatican’s response was “not intended to be a form of unjust discrimination, but rather a reminder of the truth of the liturgical rite”, the Pope said at the time.
Love Wins, however, described the Church’s decision to deny same-sex couples blessings as “a slap in the face for people around the world”.
The movement has produced a map showing all the churches offering the blessings in the coming days.
Thousands of German priests and church employees have also signed a petition calling on the Church to extend blessings to same-sex couples, while some parishes have also displayed rainbow flags outside churches.
The Catholic Church in Germany is more liberal and wealthy than many other countries and the increasingly vocal acceptance of gay couples will be hard for the Vatican to ignore, the BBC’s Damien McGuinness in Berlin says.
Same-sex marriage has been legal in Germany since 2017 and the country has also banned so-called “gay conversion therapy” for under-18s.