No they can't.If you elect to retain your shares,...

No they can't.
If you elect to retain your shares, there's nothing they can do about it.

Whether you want to or not is a decision for yourself only, unless there's a takeover/scheme of arrangement, in which case you still get to vote on it, but are bound by the outcome of that vote.

Participating in a buyback can be a great opportunity though, as it allows you to cement a capital loss which can be use to offset taxation on future capital gains.

Definitely worth thinking about carefully.

I still hold a stock that I bought into 15 years ago and have since declined to participate in multiple unmarketable parcel buybacks, purely because it wasn't a large investment and it's a constant reminder of mistakes I've made in the past and lessons learned from them.

At close of trade today, that holding is currently worth the handsome sum of $13.90. LOL