Competion in Commerce Laws of Hasagas Gevul

 https://dinonline.org/2015/08/31/opening-shop-laws-of-hasagas-gevul/

The prohibition of being yored le-umanus chavero, literally “descending to another’s profession,” or, in more simple terms, illegal competition, is derived from two distinct verses. The Gemara in Makkos (24a) derives the prohibition from the verse “he did not perform evil with his neighbor” (Tehillim 15:3), whereas the Gemara in Sanhedrin (81a) derives the same idea from the verse “he defiled his neighbor’s wife” (Yechezkel 18:11).

The Chasam Sofer (Choshen Mishpat 79) writes that the prohibition is a full Torah injunction, basing this on a number of earlier sources. Although the Beis Yosef (Choshen Mishpat 156) writes implies that there is no Torah prohibition, but only a rabbinic prohibition enacted as a tikkun olam (regulatory law), the Chasam Sofer writes that after the Sages enacted the prohibition it involves a full Torah transgression.

Certainly, the prohibition is a very grave sin, to the degree that Rabbeinu Tam (Sefer Ha-Yashar 741) even compares it with murder! As we will see, poskim treat the prohibition with appropriate stringency.