This could give those long-opposed to Walmart's planned expansion in the city of Los Angeles more ammunition: The retail giant is catching heat for its recent firing of an employee who used medical marijuana off-the-job to treat his cancer-related pain.

Joseph Casias has a tumor pressing against his skull, according to MSNBC, and uses the drug — legal in his home state of Michigan — for relief. He says he never went to his job as a Walmart associate high, but found himself terminated after he want into work one morning anyway.

“I never thought I would be terminated for this,” Casias, 29, told the website. “At first I thought, 'This wasn't true. How could this be right?'”

But a Los Angeles employment attorney, Carol Gillam, told MSNBC companies can still fire workers for marijuana use in states where the drug is a legal medical treatment. California tried to pass a law specifically banning such terminations, but it was vetoed by Gov. Arnold Schwarzenegger.

“If you're tested in the workplace, or they come to know that you have one of these cards, you can get fired,” added said Allen St. Pierre, executive director of California-based NORML.

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