I'm not stating this as fact, but the way I understand it is, employers workmans comp insurance carriers tend to be the ones who are sticklers for it. If an employer hires you after a positive test, and you get hurt, they can deny a comp claim. That tends to make employers adhere to that rule, because they would be solely responsible to pay any damages. I work as a welder, and my place couldn't care less that you smoke pot, but still have to drug test because of this. For what it's worth, I've gone 6 for 6 using the drinks sold to give you a clean urine test. It's been years, but the ones sold at GNC worked very well. The only issue I had with them was once I was told my sample was too "diluted " and had to do it again. After I drank the stuff the second time, I ate a bowl of mixed veggies with butter and parmesan cheese. This "bulked" up the sample and I passed.