Minhag ha-soḥarim are a case in point. Such laws may or may not be independently binding as social welfare legislation by virtue of dina de-malkhuta dina, the law of the land is the law. Resolution of that question is contingent upon careful analysis of the various theories propounded by early-day authorities regarding the basis and parameters of the halakhic principle of dina de-malkhuta.³⁶See, for example, R. Meir Arak, Teshuvot Imrei Yosher, II, no. 153, sec. 2, and R. David Menachem Babad, Teshuvot Ḥavaẓelet ha-Sharon, Ḥoshen Mishpat, no. 8. Such an analysis is beyond the scope of this undertaking. But, even if rent control laws are not halakhically binding per se as dina de-malkhuta, many contemporary authorities have maintained that, since those laws are generally accepted, they become implied conditions of all rental agreements.³⁷See, for example, Erekh Shai, Ḥoshen Mishpat 312:5 and Rabbi Yosef Eliyahu Henkin, Teshuvot Ivra, no. 96, sec. (1) 8 and sec. (2) 4, published in Kitvei ha-Gra’i Henkin, II (5749), 175 and 176. Cf., R. Joshua Pinchas Bombach, Teshuvot Ohel Yehoshu‘a, nos. 10-11. Rabbi Henkin apparently maintains that such laws are also valid on the basis of the intrinsic application of dina de-malkhuta. See Teshuvot Ivra, no. 96, sec. 1(4). The decision of Erekh Shai may be seen as reflecting a similar view. Regardless of whether rent control provisions are binding as dina de-malkhuta³⁸See R. Eliezer Waldenberg, Ẓiẓ Eli‘ezer, IV, no. 28, secs. 11-12, and V, no. 30, sec. 4; Piskei Din shel Batei ha-Din ha-Rabbaniyim be-Yisra’el, XVII, 195; and supra, note 37. or as minhag ha-soḥarim,³⁹An interesting aspect of that position is discussed by R. Chanoch Cohen in a short contribution to the Tishrei 5711 issue of Ha-Ma’or. A landlord demanded that his tenant either accept a sizable increase in rent or vacate the premises. Pleading the provision of the applicable rent control law, the tenant refused to do either. Thereupon the landlord declared his property to be konam vis-à-vis the tenant, i.e., he involved a principle of Jewish law that empowers an individual to render any benefit from the property impermissible to another person or persons upon pain of religious transgression. If the landlord had the halakhic power to declare a konam, the tenant would have had no choice but to vacate the premises. Rabbi Cohen asserts that, in this situation, the landlord was powerless to do so.
Without analyzing the grounds for the applicability of the principle, Rabbi Cohen asserts that dina de-malkhuta serves to vest a leasehold interest in the tenant. Since a konam is not valid if it would serve to extinguish a property interest of another individual, he argues that a konam cannot be employed to interfere with a legitimate right of tenancy. However, Rabbi Cohen’s argument is subject to dispute. Shulḥan Arukh, Yoreh De‘ah 221:1, records a controversy among earlier authorities with regard to whether a tenancy constitutes a property interest of sufficient strength to prevent a konam from becoming effective. Citing Tosafot, Arakhin 21a, Rabbi Cohen infers that all authorities would concede that a konam cannot be imposed in the presence of a tenancy in perpetuity. Assuming that is correct, it is nevertheless highly doubtful that rent control regulations have the effect of establishing a tenancy in perpetuity. any dispute between a landlord and a tenant must be resolved before a Bet Din. Despite the fact that in its salient features it is secular law that is administered, the law is binding upon Jews because dina de-malkhuta and minhag ha-soḥarim are Jewish law principles. The prohibition against recourse to arka'ot shel akum is not waived on account of the non-Jewish provenance of the particular law or regulation to be applied. Accordingly, any disputes between the contracting parties must be resolved by a Bet Din. To be sure, the judges sitting on the Bet Din may themselves not be familiar with rent control law since it is entirely secular in nature. Nor, for that matter, since they are not tradesmen, are they likely to be familiar with other matters of common trade practice. Matters of common trade practice can be established by a Bet Din by inviting expert testimony, i.e., the testimony of tradesmen who are knowledgeable regarding the customs of their trade. The provisions of rent control law can similarly be made known to the Bet Din by means of the testimony of impartial attorneys or academics who are expert in that area of law.

As noted earlier, although litigants may not voluntarily accept the jurisdiction of non-Jewish courts, nor may they agree that their disputes be adjudicated by a Bet Din on the basis of civil law, there are areas in which the particular provisions of Jewish law may be incorporated either explicitly or impliedly in a contract and made binding upon the parties. For example, Jewish law provides that rent is not due until the conclusion of the rental period. That provision is subject to variance by explicit agreement of the parties. In a locale in which it is common practice to pay rent in advance, the presumption is that the parties intend to be governed by the accepted practice. Unless otherwise stipulated, the minhag ha-soḥarim, or common trade practice, becomes an implied condition of the contract. Any dispute with regard to the existence or nature of an accepted trade practice must, of course, be adjudicated by a Bet Din. At times, the practice arises because of provisions of the legal system that are binding upon the society at large. Such laws, in effect, give birth to an accepted practice which, in turn, becomes an implied condition of contracts executed in jurisdictions in which those laws are binding.