Responsa for Shevuot 60:5

Q. In a litigation in which he was a defendant, A agreed to admit in evidence the testimony of two interested witnesses. After the witnesses testified before the court, A asked the court to reject their testimony on the ground that they were interested witnesses.
A. A's request should not be granted in view of the fact that he did not object before the testimony of the interested witnesses was presented. After witnesses present their testimony the case is closed and neither the defendant nor even the witnesses themselves can reopen it.
SOURCES: Cr. 48; Pr. 708, 915; L. 370; Rashba I, 868. Cf. Judah Minz, Responsa 6.

The custom is well established throughout the kingdom that when an individual has a complaint against the community regarding the tax he was assessed with, he must first pay that tax and, then, may summon the community to court, for the community prefers to be in possession of such tax-money. As corroborative evidence of the legality of this procedure I cite the talmudic ruling that those who pay the capitation tax for others are justified in forcing the latter in their service (B. M. 73b), since "the law of the land prevails". Moreover, since the members of the community are partners in the payment of the taxes, no individual may willfully withdraw from the partnership. Since the majority (of the members of a community) may force the minority to abide by its rulings (B. B. 8b), it may certainly force an individual to pay his taxes. The burden of proof to the contrary rests upon the person who seeks to deviate from this rule.
Since the overlord customarily collects his taxes collectively from the entire community, the exact obligation of each member of the community regarding such tax becomes determined as if already collected (the very moment the overlord demands the collective tax); and if the overlord subsequently desires to free or relieve one member at the expense of the others, he has no right to do so. Such an act on his part is not considered "law of the land," but rather constitutes outright robbery, and is, therefore, not valid.
SOURCES: Cr. 49; Pr. 708, 915; L. 371; Am II, 130. Cf. Agudah B. M. 108; Weil, Responsa 124; ibid. 133; ibid. 147; Menahem of Merseburg, Nimmukim (36); Terumat Hadeshen 341.

The custom is well established throughout the kingdom that when an individual has a complaint against the community regarding the tax he was assessed with, he must first pay that tax and, then, may summon the community to court, for the community prefers to be in possession of such tax-money. As corroborative evidence of the legality of this procedure I cite the talmudic ruling that those who pay the capitation tax for others are justified in forcing the latter in their service (B. M. 73b), since "the law of the land prevails". Moreover, since the members of the community are partners in the payment of the taxes, no individual may willfully withdraw from the partnership. Since the majority (of the members of a community) may force the minority to abide by its rulings (B. B. 8b), it may certainly force an individual to pay his taxes. The burden of proof to the contrary rests upon the person who seeks to deviate from this rule.
Since the overlord customarily collects his taxes collectively from the entire community, the exact obligation of each member of the community regarding such tax becomes determined as if already collected (the very moment the overlord demands the collective tax); and if the overlord subsequently desires to free or relieve one member at the expense of the others, he has no right to do so. Such an act on his part is not considered "law of the land," but rather constitutes outright robbery, and is, therefore, not valid.
SOURCES: Cr. 49; Pr. 708, 915; L. 371; Am II, 130. Cf. Agudah B. M. 108; Weil, Responsa 124; ibid. 133; ibid. 147; Menahem of Merseburg, Nimmukim (36); Terumat Hadeshen 341.