The general principle is: Any law that a king decrees to be universally applicable, and not merely applying to one person, is not considered robbery. But whenever he takes from one person alone in a manner that does not conform to a known law, but rather seizes the property from the person arbitrarily, it is considered to be robbery. Therefore, the king's dues collectors and his officers that sell fields with a defined tax on the fields, their sale is valid. But a personal tax is only collected from the person himself, and if they sold the field with a personal tax, behold this is not a valid sale unless the king has decreed that it is.
There11In Babylon. they taught: Rabban Simeon b. Gamaliel used to say: By three things does the world endure: justice, truth and peace.12Cf. Aboth I, 18 (Sonc. ed., p. 10). R. Muna said: The three are one, because if justice is done, truth has been effected and peace brought about; and all three are mentioned in one verse, as it is stated, Execute the judgment of truth and peace in your gates,13Zech. 8, 16. [indicating that] wherever justice is done peace is to be found (and in any case, where there is peace, there is justice.)
ת"ר מפרנסים עניי נכרים עם עניי ישראל ומבקרין חולי נכרים עם חולי ישראל וקוברין מתי נכרים עם מתי ישראל מפני דרכי שלום:
One sustains poor gentiles along with poor Jews, and one visits sick gentiles along with sick Jews, and one buries dead gentiles along with dead Jews. All this is done on account of the ways of peace, to foster peaceful relations between Jews and gentiles.
The stranger who resides with you shall be to you as one of your citizens; you shall love him as yourself, for you were strangers in the land of Egypt: I the LORD am your God. You shall not falsify measures of length, weight, or capacity. You shall have an honest balance, honest weights, an honest ephah, and an honest hin. I the LORD am your God who freed you from the land of Egypt. You shall faithfully observe all My laws and all My rules: I am the LORD.
צדק צדק תרדף JUSTICE, JUSTICE SHALT THOU PURSUE — go to (search after) a reliable court (Sifrei Devarim 144:14; Sanhedrin 32b).
למען תחיה וירשת [JUSTICE, JUSTICE SHALT THOU PURSUE] THAT THOU MAYEST LIVE, AND INHERIT [THE LAND WHICH THE LORD THY GOD GIVETH THEE] — The appointment of honest judges is sufficient merit to keep Israel in life and to settle them in security in their land (Sifrei Devarim 144:15).
But repentance, and prayer and charity annul the evil decree.13This is based on Midrash Rabbah, Bereishis 44:13.