The rule exists to stop investors locking in a gain while deferring tax indefinitely. Entering a short sale of the same or substantially identical property, an offsetting notional principal contract, or a futures or forward to deliver it, generally triggers immediate recognition of the gain.
There is a closing exception: if the offsetting transaction is closed within 30 days after year end and the original position is held unhedged and at risk for 60 days afterwards, the constructive sale can be unwound.
Collars and married puts sit in a spectrum. A protective put that leaves meaningful upside is generally fine, while a tight zero-cost collar with almost no residual exposure invites the argument, and straddle-rules can bite even where the constructive sale rule does not.
General information for the United States, not tax advice; rules change and depend on your circumstances, so take professional advice.
Related: straddle-rules, collar, protective-put, holding-period, short-selling