Responsa על בבא בתרא 143:12

Q. For many years the Jews of the entire kingdom paid their taxes to the king collectively. Then the king gave part of his kingdom to his son, and stated that henceforth the taxes of the Jews in that territory should be paid to his son. But the communities of the rest of the kingdom still demand the regular taxes from the Jews of the territory presented to the king's son.
A. The Jews of the entire kingdom became partners in the collective payment of their taxes for the reason that they were all the king's subjects and under obligation to pay their taxes to him. But, as soon as the Jews of the ceded territory ceased to be under the obligation of paying taxes to the king, the condition for the forming of the partnership no longer existed for them, and they could withdraw from the partnership (without the consent of the Jews of the rest of the kingdom). Therefore, if the king has given the entire income of the territory to his son, the Jews of that territory are under no obligation to their former associates. If, however, the king gave the territory itself to his son, but reserved the income to himself for a certain period of time, those Jews should continue to pay the taxes together with the Jews of the rest of the kingdom for that period of time.
This Responsum is addressed to R. Abraham.
SOURCES: Pr. 131; Mord. B. K. 183. Cf. Weil, Responsa 81; Moses Minz, Responsa 1; ibid. 22.

Q. A is heavily encumbered by his overlord with taxes and forced loans. He originally came to settle in T because he had made a settlement with the overlord to pay a certain amount of taxes directly to the latter, and not in partnership with the rest of the community. The community, however, demands that A pay his share of the tax on the community.
A. If A had originally separated himself from the community with the latter's full knowledge and consent, he need not cooperate with the community in the payment of its taxes; but, if he did not obtain the consent of the community, he had no right to make a separate agreement with the overlord since the custom of the community provides that all Jews be partners in the payment of the taxes. A community has a right to force a rebellious minority in its midst, to obey its customs. Furthermore, the overlord had no right to make a separate agreement with A in violation of the custom he himself had established among the Jews of his town. Such an act on the part of the overlord is not considered "law of the land", but rather constitutes downright robbery. Although according to the Talmud a king may change the customary taxation arrangements of his subjects (B. B. 143a), he is permitted to do so only when he is acting of his own accord, but not when he is urged to do so by some of his subjects. A's objection that it will be prohibitive for him to pay taxes both to the overlord and to the community, is not very serious, for he may explain to the overlord that separating oneself from the community in the payment of taxes is prohibited by our laws, that on this account one becomes involved in quarrels with the Jews of the kingdom, and that henceforth he will refuse to pay his taxes independently of the community. In such matters we are permitted to act with severity even when not directly empowered by the Talmud, as long as we conform to the spirit of the Talmud; for, were a Jew permitted to separate himself from his community, great calamities would often ensue.
SOURCES: Cr. 222; Am II, 122; Rashba I, 841; Tesh. Maim. to Kinyan, 29b. Cf. Agudah B. K. 144; Maharil, Responsa 71; Weil, Responsa 38; Menahem of Merseburg, Nimmukim (25); Moses Minz, Responsa 61d; Terumat Hadeshen 341, Isserlein, Pesakim 144.