What are the legal limits of terms and conditions?

[tzhu07]

Could a company suddenly change its Terms without any notice, and say that all current members are to be charged a $1,000 membership fee, and then just charge all credit cards it has collected through its users?

Is there some law that says users must affirmatively confirm any charges, and that those charges must be made very clear?

I've never encountered such a thing, but I'm wondering if it's possible for a company to pull a stunt like that.

 

[DeltaMac]

That would likely depend on the "reasonableness" of the change. If the change is from the present $900, to $1,000. That may be reasonable. If there is no membership fee, and goes to $1,000, that would not be reasonable, and should provide reasonable notice of opt-out, or other options, such as dropping membership, as an example.
Depends on the location/state/country, but unlikely that any jursidiction would find "no notice" with an outrageous increase in fees acceptable, or maybe not even legal.
Unless, of course, there is already provision for such changes in the previous terms and conditions. Even so, new fees in the $1,000 range should always need some advance notice.
Is it possible for a company to pull a stunt like that? Yes.
Is it likely to be challenged? Yes.
Is a company likely to get away with doing that? Without an actual case, it depends on the circumstances.