DENVER -- Pot may be legal in Colorado, but you can still be fired for using it.

Now, the state's highest court is considering whether workers' off-duty medical marijuana use is protected under an obscure state law.

Colorado's Supreme Court on Tuesday heard arguments in a case involving Brandon Coats, a quadriplegic medical marijuana patient who was fired by the Dish Network after failing a drug test in 2010, even though the company did not allege that he was impaired on the job.

Coats says his pot smoking is allowed under a little-known state law intended to protect employees from being fired for legal activities off the clock. But the company argues that because pot remains illegal at the federal level, medical marijuana isn't covered by the state law.

The case is being watched closely around the country and could have big implications for pot smokers in the first state to legalize recreational sales of the drug. Though the Coats case involves medical marijuana, the court's decision could also affect how companies treat employees who use the drug recreationally.

The six justices fired a barrage of questions at attorneys from both sides, but they offered no glimpses into their opinions on the matter. It could be weeks or months before they issue their ruling.

Tuesday's arguments highlighted the clash between state laws that are increasingly accepting of marijuana use and employers' drug-free policies that won't tolerate it.

"This case need not be an endorsement or an indictment of medical marijuana" but a chance to set standards for employee conduct, Dish attorney Meghan Martinez told the justices. "It's a zero-tolerance policy. It doesn't matter if he was impaired or not."

Coats, 35, was paralyzed in a car crash as a teenager and has been a medical marijuana patient since 2009, when he discovered that pot helped calm violent muscle spasms that were making it difficult to work. Coats worked for three years as a telephone operator with Dish before he failed a random drug test in 2010 and was fired. He said he told his supervisors in advance that he probably would fail the test.

Coats said he never got high at work. But pot's intoxicating chemical, THC, can stay in the system for weeks.

"He smoked marijuana while he was at home and then he crossed the threshold and came to work at Dish with THC in his system," Martinez said. "The use is the effects."

Coats' case comes to the justices after a trial court judge and Colorado's appeals court upheld his firing, saying pot can't be considered lawful if it is outlawed at the federal level. Both courts said the state's medical marijuana amendment provided exemptions from criminal prosecution for pot use but did not guarantee the right to use it.

Coats' attorney, Michael Evans, told the justices Tuesday that while medical pot is federally illegal, it must be considered legal under state law.

"We're getting very confused and mixed messages from everywhere," Evans said. He asked the court to issue a narrow ruling that would apply to people like Coats: those in nonhazardous jobs who are not impaired at work and whose employers don't have federal contracts that could be jeopardized.

Michael Francisco, an attorney for the state, said a Coats victory would make Colorado companies liable by being unable to fire those who have broken federal law.

A patchwork of laws about marijuana across the country and the conflict between state and federal laws has left the issue unclear. Twenty-three states and Washington, D.C., allow medical marijuana, but courts have ruled against employees who say their pot use is protected. Colorado and Washington state also now allow recreational sales, though court cases so far have involved medical patients.

Colorado's constitution specifically says that employers don't have to amend their policies to accommodate employees' marijuana use. But Arizona law, for example, says workers can't be punished for lawfully using medical marijuana unless it would jeopardize an employer's federal contract.

State Supreme Courts in California, Montana and Washington state have all ruled against fired patients. A lawsuit filed by a physician assistant in New Mexico who said she was fired for using medical marijuana, which helps with her post-traumatic stress disorder, is still pending.

Denver labour and employment attorney Vance Knapp said a Coats win "would turn employment policies into chaos." Other states with lawful-activity laws could see them challenged as a result.

Coats, who has been unable to find steady work because of his marijuana use, said after the hearing that he was hopeful he would prevail. At the very least, he said, the court will offer clarity on the issue.

"I'm not going to be able to get a job in the near future, so if I can fight the fight and hopefully change that, that's what I am going to do," he said.