Pruning thuja plicata
 

I have been told it is possible to hard prune the bottom 6ft of thuja
plicata as new growth is possible without seriously damaging the tree.
Others tell me that pruning back to the brown branches will damage the tree.
I wish to recover some lost ground space as the trees have been neglected
over the years. The trees are south-facing, so is it possible to prune
these trees (6ft up from ground level, and up to 6 ft towards the main
trunk)?

Regards