About the legality, they can pretty much do whatever they want but I wouldn’t be surprised if some Netflix customer could won a court case in certain jurisdictions. Even so, I hardly think they’d get much more than a small refund, so it wouldn’t be worth it.
Legal doesn't mean it's actually right or rational, and ViacomCBS, its Nat. Amusements holding company, plus Netflix to a lesser extent, are all looking quite stupid, throttling the goose laying the golden eggs, and painting themselves into a corner by having too many rival streaming services, with the actual content getting stretched too thin.
It emerged as a concern some years ago, but now most of the audience is feeling the pinch from streaming service pissing matches like this and its damaging IP brands (Trek got suddenly denied 90% of its global audience for 12 to 18 months easily, if we're lucky).