As recreational cannabis sales begin Jan. 1, one fact is sometimes overlooked: Employers still can fire workers for using it on- or off-duty.

State law gives employers full authority to impose any drug prohibitions they wish, despite it being legal in Colorado for adults to possess and consume marijuana.

“Employers hold all the cards,” said Curtis Graves, a staff attorney for the Mountain States Employers Council.

So you smoke only off-duty? Not good enough. Consuming just at home provides no protection if your workplace drug test comes back positive for marijuana.

Many employees may be enjoying a false sense of security stemming from passage last year of Amendment 64, which legalized marijuana possession for adults in Colorado.

“Right now there is a great deal of confusion,” said attorney Danielle Urban of labor-law firm Fisher & Phillips in Denver. “People are surprised to learn that they can lose their jobs.”

Amid the euphoria of approving legal pot, some cannabis enthusiasts may have overlooked a key piece of fine print in Amendment 64.

Nothing in the law will “affect the ability of employers to have policies restricting the use of marijuana by employees,” the amendment states.

That includes getting high at work or even after hours, according to legal experts and judicial rulings.

Tests can’t determine exactly when pot was ingested. Marijuana metabolites can remain in the human body for weeks, so employers don’t know whether a positive test resulted from on- or off-duty use. Nor do they care, if they have a strict no-drug policy.

Mason Tvert, who co-directed the Amendment 64 campaign, said a double standard exists because employers would almost never sanction a worker for off-duty alcohol use, unless it was affecting job performance. Yet with cannabis consumption, penalties can result even if employees use it legally off-duty and are not impaired at work.

“It’s really irrational to punish employees for engaging in lawful activities outside of the workplace,” Tvert said.

Despite legalization of recreational use in Colorado, it is still a taboo subject for employers. Several Denver-area businesses declined to comment about their marijuana policies.

A couple of companies, though, say their position won’t change, at least initially.

“We have discussed the new law and how it’s going to impact our business with recruitment and overall operations for quite some time,” said Jeremy Ostermiller, CEO of Denver-based Altitude Digital. “There is still uncertainty how the federal government will respond to the states’ new legal-marijuana laws. We don’t have rules concerning off-hours marijuana use. At this time, we are not changing our drug-testing policy, but we embrace and fully support the new Colorado law.”

Altitude Digital, which employs 50, does not test its workers for drugs.

Ostermiller said he worked with pot-friendly artists such as Snoop Lion and Cypress Hill prior to starting his online video marketing business.

“Many believe their marijuana use has fostered creativity, an important and valuable asset to any business,” Ostermiller said. “While there is a lot of misinformation about marijuana use, especially how it affects the body, Altitude Digital encourages creativity by cultivating a fun and collaborative company culture.”

Denver-based Spire Media, a Web designing and consulting firm, also doesn’t test its employees for marijuana.

“I’m not going to fire somebody if they smoke pot, but I don’t want them doing it in the office,” said Spire CEO Mike Gellman.

His position won’t change after the new law goes into effect, he says.

“I know personally I wouldn’t be able to do my job if I smoked pot,” Gellman said. “But I know some people can program and do better programming while smoking pot, and that’s fair.”

Graves, of the Mountain States Employers Council, said employers in high-turnover service industries such as retail, hotel, restaurant and casino may be less inclined to use routine drug screenings because they already are challenged with maintaining staffing levels.

In addition to Amendment 64’s clear language that gives employers full discretion in setting marijuana policies, a Colorado court case this year affirmed an employer’s right to prohibit medical marijuana use, even off-duty for employees with registered medical status.

Dish customer-service employee Brandon Coats, a quadriplegic, sued Dish after the satellite-TV company fired him for testing positive for marijuana in a random drug test.

Coats acknowledged that he used legal medical marijuana off-duty to help control muscle spasms but said he was never under the influence at work. Nonetheless, Dish fired him after the positive test.

In a precedent-setting decision, the Colorado Court of Appeals upheld the firing. The court said that since marijuana is illegal under federal law, employers can sanction their workers and are not bound by Colorado’s Lawful Off-Duty Activities Statute, which otherwise prevents employers from interfering in employees’ nonwork activities.

Coats’ attorney, Michael Evans, has appealed the ruling to the Colorado Supreme Court.

“Unless you’ve got a guy who is obviously impaired,” Evans said, “you should hold off on terminating him.”

Steve Raabe: 303-954-1948, sraabe@denverpost.com or twitter.com/steveraabedp