Answered by Shaykh Faraz Rabbani
Do muslim cab drivers refusing passengers who carry alcohol have a case?
Walaikum assalam wa rahmatullah,
In the Hanafi school, this is not from “assisting in sin,” because the service they themselves are providing–taking the customer from point A to point B–is permissible, as is the very act of allowing them to put “something” in the trunk. Please search SunniPath Answers (http://qa.sunnipath.com) for related answers on “assisting in sin.” [Ref: Ibn Abidin, Radd al-Muhtar]
If they are working for a cab company, then they would be religiously to follow company regulations on such matters, as these are part of their contractual agreement with their employer.
And Allah alone gives success.