What is the ruling on working a job where my salary partly comes from a business selling non-halal products?

It depends on how directly your role is tied to the non-halal part of the business. Scholars generally distinguish between working directly in the prohibited activity itself — being the one who handles, sells, or manages pork or alcohol specifically, for example — which is not permissible, versus holding a genuinely separate, lawful role (general accounting, IT, HR, logistics unrelated to the haram product line) at a company whose overall business includes some non-halal segments, which is treated more leniently by many scholars, particularly when the haram segment is a minor part of a larger, mostly lawful business.

The closer your specific duties and the portion of salary tied to them get to the non-halal segment, the more caution is warranted — a cashier who personally rings up pork and alcohol sales at a general supermarket is in a genuinely different position than a company-wide payroll administrator whose salary isn't traceable to any one product line. Where it's a close call, or where a large or growing share of the business is the non-halal segment, most scholars would advise actively looking to transition to a fully halal role or employer rather than treating the gray area as permanently comfortable.

Source: general fiqh principle distinguishing direct participation in haram activity from incidental employment at a mixed-business employer; applied by analogy from broader rulings on cooperating in sin (Quran 5:2) and permissible mixed-income employment.