Individuals who have legally emigrated to the US are being denied citizenship by the federal government for working in state-legalized cannabis markets.

Although recreational cannabis has been legal in Colorado for five years now, working for the industry is still risky. A number of legal US residents of Denver found that out the hard way recently when they were denied full citizenship after revealing to US Citizenship and Immigration Services (USCIS) that they were employed by the state's marijuana industry.

One of those individuals was Oswaldo Barrientos, who emigrated to the US from El Salvador nearly 30 years ago with his mother. Barrrientos said he's had a Green Card since he was 13, and he hoped he would finally be able to become a full US citizen. However, the US federal government denied Barrientos' application for citizenship, citing a lack of "good moral character" due to his employment in Colorado's cannabis industry.

"Twenty-nine years of me being here, not breaking the law in any way, at least on a state level. I've done everything by the book," Barrientos told ABC News. "I thought I was a shoe-in."

As Barrientos' immigration lawyer Bryce Downer explained, the interview process that citizenship applicants have to go through are designed to make legal cannabis workers  confess to committing federal crimes. That's more than enough to deny a request for citizenship, and could even be used to lay charges.

"By the end, they've led you down this path to openly admitting you've engaged in felonious activities and you've essentially admitted to drug trafficking, drug distribution and drug manufacturing," said Downer.

As far as immigration officials are concerned, however, they're just doing their job. Denying citizenship to those who work in state legal cannabis businesses is well within their purview, said USCIS spokesperson Deborah Cannon.

"Marijuana is illegal under federal law, and, as a federal agency, USCIS is required to adjudicate based upon federal law," said Cannon in a statement.

In response to cases against Barrientos' and others, Denver City Mayor Michael Hancock has issued a letter to US Attorney General William Barr asking the Department of Justice to address this "injustice" and allow immigrants working in the state's cannabis industry to become citizens.

"Denver believes hardworking and law-abiding immigrants should be allowed to participate in the legal cannabis industry without fear that such participation will disqualify them for lawful residency in the United States or prevent the opportunity to obtain permanent citizenship," Hancock wrote. "We respectfully request that the US Department of Justice uphold Colorado's states' rights by respecting our voters and providing guidance to all DOJ employees clearly indicating that legal immigrants shall not be penalized for working in the legitimate cannabis industry."

Barr is opposed to cannabis legalization, but he has said that he would not interfere with states that have legal cannabis. Whether he'll stick up for members of the industry like Barrientos remains uncertain.