Cross-lease owners are being warned a Court of Appeal ruling may curb current veto powers.
A decision made last week could make it harder for a neighbour of a cross-lease property to withhold consent to proposed alterations.
It shifts the old power balance, with 215,000 cross-leases owned nationwide.
Pidgeon Judd Law Director Joanna Pidgeon told Mike Hosking changes can't be vetoed by neighbours unless deemed reasonable.
She says parties need to reflect on what both people want and what a reasonable person would decide.
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