Responsa for Bava Batra 43:2

Q. The community of T, with the consent of (R. Meir's relative) Kohen Zedek, decreed: a) that anyone who moves out of T may not return to it in order to lend additional funds to his debtors, for the purpose of fortifying his investments with them, without the knowledge and consent of the community, the latter having to determine whether or not such debts can be collected without lending additional funds to the debtors; b) that if the debts can be so collected, the non-resident creditor be not permitted to lend additional funds to the his debtors; c) that in case a member of the community will be willing to take over the investments of such creditor, the latter be forced to transfer such investments to the former; and d) that if anyone is found transgressing this decree and lending additional funds to his debtors without the knowledge and consent of the community, he should pay on all of his money that can be found a tax of six Cologne pennies per mark. A was discovered to have transgressed this decree.
A. If A was a resident of T when the aforesaid ordinance was passed, whether he supported the measure, accepted it tacitly, or openly protested against it, he is bound by it even though he subsequently moved out of T. For a person's protests against an ordinance designed for the public benefit and passed by a majority vote of the worthy members of the community are of no avail. Thus the ordinance of Rabbenu Gershom reads as follows: "If the residents of a city have established an ordinance for the benefit of the community, for the benefit of the poor, or for any other useful purpose, and most of the worthy ones have agreed to it, the others may not void such ordinance and may not demand to take the matter to court, for no court may sit in such a case, because everything depends on the opinion of the prominent men of the city, in accordance with the custom of the ancients, or as an emergency measure."
If A, however, moved out of T before the ordinance was passed, he is to be governed only by talmudic law and by customs generally accepted by the communities, while any restrictive measure adopted by the community of T after A moved out is not binding on him. A community may force a dissenting minority and all those who subsequently come to settle in the town, to accept its decrees and ordinances. But a community possesses no authority over a person who moved out of town before the decrees and ordinances were passed, and who does not live there any longer. Therefore, if A had had ample opportunity, since he left T, to force his debtors to replay their debts to him, and failed to do so, he must pay the community taxes on such debts. But if he was unable to collect these debts, the custom is well established in all communities not to tax such debts. Any local ordinance in opposition to such custom is not binding on a non-resident who was a non-resident at the time the ordinance was passed. But, if the community representatives claim that A has had ample opportunity to force collection of his debts, and A denies such claim, the latter must take an oath to bolster his denial.
This responsum is addressed to "my relative Kohen Zedek."
SOURCES: Am II, 140; Mordecai Hagadol, p. 300a.

Q. A [moved out of T but nevertheless] lent money to his customers there. The community of T, therefore, forced him to pay taxes. He now claims that the community had no right to collect these taxes from him since he had made no new investments in T but merely had lent additional funds to his customers in order to be able to collect his old debts from them. The community representatives aver that A could have collected his debts without lending additional funds to his debtors.
A. If A could not have collected his debts unless he had lent additional funds to his debtors, he had a right to lend them such funds, and these transactions should have been tax-free. The members of the community, as interested parties, are not qualified to serve as witnesses in this matter. Therefore, either every member of the community must take an oath to support the claim of its representatives, or the community must permit A to take an oath in support of his contention. However, if the community can produce even a single, independent, witness — one who has no financial interest in this trial, or one from whom the community shall agree to take a certain specified amount as his share of the tax regardless of the outcome of this trial — in support of the claims of the representatives, or to the effect that A freed the community from the obligation of taking an oath, no oath will be required.
SOURCES: Cr. 156.

A, however, must pay his "tithe" to the community charity fund, from the profits he earned in T.