What are the limits of Dina Dmalchusa (specifically financial Dina Dmalchusa, unlike this question which deals with non-financial dina dmalchusa)?
In general, dina dmalchusa means one must pay taxes and obey financial laws. Does that apply to any unreasonable tax that a tyrant wishes to impose on his country?
If a dictator ordered all countrymen to give all his money to the government, is someone who keeps some money hidden under the mattress pasul for eidus?
This was addressed long ago and is codified by Rambam.
If it's a fair tax upon everyone, we say dina d'malchusa dina. If the standard law is that if someone is found guilty of treason then the king confiscates all his property, that's still fair. But if the king can randomly seize anyone's stuff for himself just because he feels like it, that's strongarming (chamas), not dina d'malchusa dina.
I'd asked a halachic authority if Iraq under Sadam Hussein would have been considered dina d'malchusa dina, he said absolutely not. I asked where exactly the line was drawn, he said that was a government with no yashrus whatsoever, he knew it when he saw it.
In the early days of Communism, Rabbi Moshe Feinstein felt that dina d'malchusa still applied to a degree; the government was valid, though wrong to persecute religion. Though he got out of Russia several years before Stalin became premier ...
