You certainly can advise your contractors. You can stipulate in your contract that the work must be completed in a certain way. As this relates to uber I'm sure that they tell all their drivers to not break the law (covers speeding, running red lights, and also discrimination).

The onus in this case is on the users to out the drivers to Uber through the review system. Maybe they need a submit button on the review page that says 'my driver broke the law'.