He says he's battled sinus cancer and a brain tumor for eleven years. Most of the time, he's treated his pain with a concoction of pain killers. But when Michigan legalized marijuana for medical purposes, he signed up. Casias is one of the state's 10,022 registered patients.

In the fall of 2009, Casias fell while on the job. He says Wal-Mart required him to take a drug test, which came back positive for a controlled substance. Casias was fired.

On Sunday, dozens of people protested outside of Wal-Mart, saying what the company did wasn't legal. But a spokesperson for the retailer disagrees. The company says the test don't say which drug was found in Casias' system; all it shows is that a controlled substance was found, which is a violation of its drug-free policy.

The Michigan Community Health Department, which oversees the program, says if an employee is taking marijuana for medical purposes, they cannot be terminated for drug use. However, the health department doesn't get involved in legal matters, and a spokesperson says if Casias wants his job back, he'll probably have to get a lawyer.