Medical marijuana and the ol' urine test?

I have chronic back problems and am trying to get a doctor to prescribe bud as opposed to all the other pain killers that are way worse for you. My question is if you have a doctors note can your employer terminate you if you have in your system when you do the urine test (even if the doctor can verify you wernt baked when you gave the sample)? I have been at my job 18 years and cant afford to lose it, But cant see why i cant blaze a joint instead of taking vic or oxy. I'm in cali and i know iour laws are a little difficult. Thanks!

If you have a medical marijuana card, your place of employment cannot fire you solely because of your marijuana use.

Good luck man! Happy blazin!