#Legal:
* Judge orders them to comply, if they refuse they can be considered to be in contempt and incarcerated for a de facto arbitrary period of time at the judge's discretion (vide https://en.wikipedia.org/wiki/H._Beatty_Chadwick incarcerated for contempt for 14 years just because the judge suspected he had funds that apparently he didn't have, also Terrell Geiger http://articles.chicagotribune.com/2011-10-07/news/ct-met-lo...)
* Civil forfeiture. The state can just de facto steal every single item those people have and leave them unable to fight that in court (not that it would make much difference)
* Involuntary commitment. They can just be committed into a psychiatric institution where they can be drugged against their will and even tortured. This can be extended to an arbitrarily long period of time
* They can have their children taken away
* IRS can just accuse them of an astronomical tax debt, take all of their possessions and leave them effectively unable to get legal representation (not that it would make much difference)
#"Illegal":
* Just detain them in a secret facility and do with them as they dam well please
TLDR: The state does with you what it damn well pleases and there's nothing you can really do about it. Granted this usually doesn't happen but that's just because the stakes usually aren't that high.