When the US dollar crashes.
"the US will be prepared ahead of time with a new, electronic currency. This will serve three purposes:
It will allow the US government to blame paper currencies for the crash, in order to distract the public from recognising that the government itself is the culprit.
It will allow the US government to create a currency system that disallows the holding of tradable currency by the population—that is, a debit card would be created by banks through which all transactions must pass, assuring that all transactions are processed by (and thereby subject to the control of) a bank.
It will allow the US government to have knowledge of every penny earned and spent by any individual or organization, allowing for direct-debit income taxation."
http://www.zerohedge.com/news/2015-04-25/what-will-happen-you-when-dollar-collapses
Personally, ZH.com is hard to take seriously. They are heavily biased and fringe conspiracy theory.