[Edited due to subsequent information received]
Like KiwiPaul, I’m not sure what the law was when this by-law was agreed upon but I would say it would certainly be worth a phone call to an experienced strata lawyer to see if this land grab holds up.
The fact that the beneficiaries won’t pay any additional levies makes the whole thing even more suspect. You could apply for a revision of Unit Entitlements on those grounds alone.
Any individual or group of individuals can challenge the status quo at the CTTT. I would get together with like-minded people, tell the free parkers that everything is about to change, whether they like it or not, and they can sit down and negotiate a reasonable compromise now or risk losing their car parking entirely when the by-law is bounced out by the CTTT.