The Obligation to pay when Informing on Another Yid

My neighbor is renovating without a permit. May I inform the authorities? 

Informing on a fellow Jew is called mesirah. It is forbidden to inform the authorities that a Jewish neighbor (or any Jew for that matter) is making renovations to their property without a permit, unless it poses a danger; if that is the case, a Rav should be consulted first in order to determine whether it’s permissible to report them.

If one does inform the authorities in a situation where it doesn't pose a danger, and it results in the neighbor receiving a summons, the informer might be obligated to compensate the neighbor for any penalties incurred, even though it came about indirectly. This is based on the halachic principle of dina d’garmi (a proximate cause, in contrast to grama which is a remote cause. The result of a garmi act has greater immediacy, proximity or predictability than that of grama; one is liable for damages that are an obvious result of one’s actions, even if they occur indirectly. The precise definition of garmi is the subject of debate among poskim).

Moreover, if the one setting out to renovate consulted his neighbors prior to beginning work and received their consent, and then one of them has a change of heart and informs the authorities, it is a case of hotzi hotzaos al piv (he spent money based on his word). The informer may then be liable for the additional financial losses incurred by the neighbor due to the interrupted work—such as money paid to the contractor, etc.—since he gave the go-ahead for the renovations, and then caused them to be halted.

Since there are a number of halachic variables, a beis din would have to determine which costs the informant is liable for; sometimes the informant may be absolved on the grounds that he mistakenly thought that this mesirah was permitted—but that issue would also have to be addressed by the beis din. #488

https://halacha2go.com?number=488

Practical Halacha: One minute a day. By Horav Yosef Yeshaya Braun, shlita, Mara D'asra and member of the Badatz of Crown Heights.