The Colorado Supreme Court on Tuesday heard arguments in a lawsuit brought by an employee of Dish Network who was dismissed after he tested positive for marijuana. The employee, Brandon Coats, has a state-issued medical marijuana license.

In April, an appellate court in Colorado ruled employees can be fired for testing positive for marijuana. Coats was fired by Dish Network in 2010 after he tested positive for marijuana—a violation of company policy. Coats is a quadriplegic. He said he never used marijuana on the job, and argued Dish Network’s policy violated a state law that bans companies from firing employees for off-duty, lawful activities.

Colorado legalized medical marijuana in 2000, and passed a law legalizing recreational marijuana in 2012. The appellate court ruling affirmed a lower court decision that marijuana use does not qualify as lawful because it is still illegal under federal law.

“We are not arguing that it’s a constitutional right, but we are arguing that it’s lawful,” Michael Evans, Mr. Coats’s lawyer, said Tuesday in court.

The case is being closely watched around the country, The Wall Street Journal reports. Medical marijuana is legal in 22 other states and the District of Columbia. Recreational marijuana is also legal in Washington state.

The court is likely to first answer the question of whether using marijuana can be considered a lawful activity if it is banned under federal law. Evans argued that employment law is a state matter. If the Colorado legislature had wanted to include federal law, it would have done so, he said. Michael Francisco, a lawyer representing the state, said according to this line of reasoning, an employer could be held liable for dismissing an employee who has violated federal law. He called this “an absurd result.”

The justices could take weeks to issue a written opinion, according to The Denver Post.