Halakhah zu Wajikra 5:1

2. A person is permitted to place a cherem in the synagogue on anyone who knows testimony for him to come and testify. He cannot, however, force them to swear. If they don’t testify, they will carry their sin. Nevertheless, if the court sees a need to have them swear to say the truth, they may do so. See earlier 17:3 and later 71:7-8. There are those that say that when a cherem is placed, even relatives and the party himself must testify. There are those that disagree and this is the primary ruling. See Yoreh Deah Siman 232 regarding a king who commands the placement of a cherem for testimony.

Rabbi Waldenberg notes that Jewish law also provides that the Bet Din may compel testimony which would otherwise involve a breach of personal or professional confidence. The obligation born of the commandment "… he who is a witness … if he does not inform, he should bear his iniquity" (Leviticus 5:1) supersedes the obligation to respect the privacy of others. It would seem that in such cases Jewish law would require that testimony of this nature be heard in camera in order that matters of a personal nature not be overheard by persons who have no "need to know." This was indeed the ruling of the Israeli Supreme Rabbinical Court, Piskei Din Rabbaniyim, IX, 331, in a related case.

The question of whether testimony by a physician before a Bet Din constitutes a violation of the Hippocratic oath is also discussed by Rabbi Baruch Rakover, presently a member of the rabbinical court of Haifa, in No'am, vol. II (5719). Rabbi Rakover concludes that the physician is forbidden to testify by virtue of his oath in situations in which he is the sole witness. Moreover, even when the witnesses are two or more in number, argues Rabbi Rakover, the physician may not testify unless summoned to do so by one of the litigants. Testimony is ordinarily obligatory by virtue of the specific biblical commandment, "if he shall not testify he shall bear his iniquity" (Leviticus 5:1). This commandment is understood as requiring testimony only when demanded by a litigant. In the absence of a demand on the part of a litigant the witness is required to come forward by virtue of a general obligation to prevent loss or damage to one's fellow. The requirement to give testimony voluntarily under such circumstances is recorded in Yoreh De'ah 239:7. Rema rules that since the obligation to testify under such circumstances is not explicitly stated in Scripture a prior oath not to testify is valid and must be annulled before giving testimony.