''To us the maunga is a wāhi tapu (sacred place). The last thing we want is to come out of our marae and see this monstrosity of a stainless steel pole sitting on top of our maunga.''
At two previous community meetings landowners had put forward other options but they had been rejected as unworkable.
However, Rapana said an expert had told him the other sites could be made to work, but would be more costly.
Three members of the group visited the landowners on Monday and asked them to stop the project.
Rapana said the title owners had been there for many years and treated the maunga with utmost respect, but said a contract had already been signed and referred the group to the RCG.
Group members then called the RCG but got a curt response with the manager saying hapū had already been consulted and they needed to sort the issue out among themselves.
With the more diplomatic options exhausted all that was left to the group was a ''full scale occupation'' of the maunga and its base, Rapana said.
Later on Monday the RCG called a halt to work on the cell site.
Engagement manager Caitlin Metz said the RCG had been talking with local iwi and hapū since October 2018 with a community hui, an iwi hui and ongoing engagement since then.
''We appreciate that the hapū have differing views ... We have ceased work on the site as we respect the need for the hapū to address the matter internally,'' she said.
Metz said five alternative sites were investigated but only Whakarongorua would give coverage to the entire valley. A site suggested at the community hui was also investigated but from there Whakarongorua would block the signal from reaching several areas.
It was RCG's understanding that all hapū in the valley — including Ngāi Tāwake ki te Moana, Ngāti Toro, Te Ngahengahe, Te Popoto, Ngāti Hao and Te Honihoni — had attended the December 2018 hui, she said.
The Whakarongorua Action Group will meet at Mokonuiārangi Marae in Utakura Valley at 10am this Saturday to decide a way forward.
Rapana said the group had taken inspiration from the occupation at Ihumātao, but hapū members had been following developments at Whakarongorua long before the Auckland protests.
They had been prompted to act after contractors started bringing machinery on to the site on Friday.
The Utakura Valley, which forks part of the Twin Coast Cycle Trail, was identified as a priority area under the Government's Mobile Black Spots Fund.
The programme entails the Government working with Vodafone, Spark and 2degrees to build 27 new cell sites around the Far North, including popular tourist spots currently without mobile coverage.