Protesters who broke into St Joseph's Church in the docks area of Belfast are challenging Catholic leaders to debate the future of the building with them.
Protesters in St Joseph's Church in Belfast's dockland
They have been occupying the grade B listed church since Sunday and say they intend to stay for three days.
Fr John McManus of Down and Connor diocese said he was "saddened and disappointed by the irresponsible act".
The Catholic Church closed St Joseph's in 2001 because the "congregation was too small to justify keeping it open".
As a listed building, the church comes under the protection of the Department of the Environment.
Campaigners said urgent repairs were needed if the building was to survive.
Paul McLaughlin of the Save St Joseph's Campaign said the DoE should enforce the regulations and compel the Catholic Church to make the necessary repairs.
"But today is also about highlighting the fact that a complete faith community of 150 people has been neglected by the Catholic Church for five years," he said.
"We have been forced to do this because no-one will speak to us, so what we are saying is, we are taking back our church."
Fr McManus said the church was mindful of its responsibility as a historic building owner. He said the situation would be kept under review.
"It's deeply regrettable that the initiatives of those who worked so hard to find a sustainable and suitable future for the building were lost," he said.
The DoE's Environment and Heritage Service (EHS) said it had been working with Down and Connor Diocese to encourage the protection of the building.
A Heritage Service spokesperson said: "There are proposals to have the building taken over and refurbished by a preservation trust.
"EHS would welcome any such proposals (which) might attract grant aid."