The documentary that accompanied the recent ITV Drama "Mr Bates vs The Post Office" provides a good overview. Listening to the actual people impacted by this is heart breaking.
PCI DSS is not voluntary if you transmit, store or process credit cards.
It is enforced through contract, typically for a merchant through their relationship with their bank, for service providers via the contract with the merchant.
Whilst this adds no additional information this editorial is from a provincial newspaper in NZ. It is notable as it could be seen to represent the sentiments of NZ's agricultural 'mid-west' towards the actions that have occurred in NZ at the request of the US.