I would be fascinated to know the legalities of this.
My first thoughts are, it's a small step from refusing owners/tenants access for one night, to booking the pool out for a week, a month, a year, permanently. It's likely to be the same tenet under the law.
Unless I am mistaken, changes to common areas require raising at an AGM or an EGM (Extraordinary General Meeting) at which a quorum must be present and a certain percentage must vote in favour.
If I was an owner, I would be speaking to the Juristic Manager/Management Company to understand in full detail what the benefits to the co-owners is and what process they followed to book it out to a private function.