They can withhold a bank license I guess, something along those lines.    Just exchanging data isnt illegal but governments have got upset with the idea people have been allowed to exchange value without giving them a cut of every transaction as is the case with conventional paper money issued centrally.
  It seems increasingly likely we will all get a taste of the Chinese model of capital control if governments are funded by inflation then by necessity it'll start to be the case we confiscate capital not just not the idea of income taxes.   I think Elizabeth Warren states this idea explicitly but it doesn't especially matter as its already in the lay of the land now and as a trend.   This is the consequence of excessive debts and uncontrolled spending fiscally to win votes, float politics, etc.

They want the same thing for money and spending as they already do with your family connections.  They want information to sell and target advertising at you based on personal information you wouldn't otherwise freely give so if you like donuts every Tuesday, they want to know that so it can be added to their file on you.