That’s how by-laws are created under the terms of the Strata Schemes Management Act. Does your committee operate under its own set of laws?
Have they explained how they (whoever “they” are) think it works? Do they think they can just issue edicts and ban residents from areas of common property?
Even if there is a catch-all by-law that says access to the pool could be controlled by decisions of the committee, as and when required, those decision would still have to be on a strata committee agenda, voted on and minuted.
So, what do your by-laws say, exactly? (please, the exact wording)
If there is no by-law regarding access to the pool, then the committee and/or managers are going way beyond their remit.
If there is a by-law, then it should establish the rules in writing so that everyone knows what they are.