As a general rule, informing on a Jew (mesira) to the secular authorities is forbidden and one who does so is referred to as a moser. This applies even to those who are otherwise sinful, wicked, and seemingly deserving to be informed upon.1 In fact, one who informs upon another Jew might even be (theoretically!) subject to the death penalty and permitted to be killed by anyone at any time.2 This is often true even if one’s informing merely results in the secular authorities seizing another Jew’s money and possessions.3 Indeed, a moser who causes the secular authorities to seize the property of a fellow Jew is considered to be a rodef, one who pursues a Jew to kill him.4 A moser is disqualified from serving as a witness in ritual matters,5 has no share in the World to Come,6 and is no longer counted among the Jewish people.7 One does not need eyewitness testimony to declare someone a moser; circumstantial evidence is sufficient for this purpose.8
One who works for the government in a position that requires one to report tax evasion and other irregularities is permitted to inform on a Jew who clearly violates the law.9 Based on the halachic requirement of dina d’malchuta dina, that one must obey the laws of the land one lives in, one who works for the police or in a similar position is permitted to enforce the law even upon a fellow Jew, as appropriate.10
One who knows of Jews who are counterfeiting money is required to report them to the authorities.11 So, too, Jews who engage in activities that will endanger the well-being of the Jewish community may be informed upon as well.12
If gentiles seize a group of Jews and demand that they choose one of them to be handed over to be killed or else the entire group will be killed, they must respond “kill us all.”13
One who is forced under duress to be moser is exempt from any liability or punishment.14
All landlord-tenant related disputes should be settled between the parties or with the assistance of a beit din and not through the secular authorities.15 A person who provides ritual services, such as a butcher or shochet, and is found to be cheating his customers should only be brought to the secular authorities as a last resort.16 As a general rule, it is forbidden to take a Jew to the secular authorities, especially if the resulting punishment would be incompatible with Jewish law.17
If one has information that a certain person is a danger to society or is otherwise likely to harm others, then one is obligated to promptly report them to the authorities.18 For example, one who knows that a fellow Jew is a dangerous driver, or that he drives without having a driver’s license, may be reported to the police.19 It is permitted to report to the authorities a Jew who is engaging in activities that damage one’s property, if he fails to heed one’s warnings.20 A doctor (or rabbi, for that matter) is permitted to inform the secular authorities if he suspects that a child is being abused21 or raped22 at home, and the like.
It might just be that the prohibition against mesira was enacted due to the brutality of the secular authorities common in past times, and even today in much of the undeveloped world.23 In the event that no physical harm or extremely unfair penalties will be laid upon a Jew if one were to inform on him to the secular authorities, as is the case in most Western democracies, then the horrible label of moser would not be applicable. It may even be outright permissible to report a Jew in such countries when justified.24 Although even in Israel it is forbidden to take another Jew to a secular court, one who does so, or otherwise reports Jews to the authorities, may not have actually transgressed the prohibition of mesira. This is because the parameters of mesira in a secular Jewish state are complicated, and are beyond the scope of this article.25
1 CM 388:9.
2 CM 388:10.
3 Rambam, Hilchot Chovel U’mazik 8:10-11; Rambam, Hilchot Teshuva 3:12.
4 Teshuvot Harosh 17:1.
5 CM 388:8.
6 CM 388:9.
7 Rambam , Hilchot Mamrim 2:2.
8 Rivash 37.
9 Shevet Halevi 2:58.
10 Maharam Alshich 66.
11 Rema, CM 388:12.
12 CM 388:8,9,12; Taz, YD 157:8.
13 Rambam, Hilchot Yesodei Hatorah 5:5.
14 CM 388:2.
15 Mishne Halachot 9:327.
16 Igrot Moshe, CM 1:8.
17 Igrot Moshe, OC 5:9.
18 Shach, CM 388:59; Shach, CM 345:45.
19 Teshuvot V’hanhagot 1:850.
20 Beit Yitzchak, CM 77; Divrei Chaim 1:46.
21 Nishmat Avraham, CM 4:388.
22 Tzitz Eliezer 19:52.
23 Sma, CM 388:29.
24 Aruch Hashulchan, CM 388:7. See http://www.jlaw.com/Articles/mesiralaw2.html at length.
25 Tzitz Eliezer 19:52.