The U.S. Department of Transportation announced Monday it will continue to treat marijuana use as a violation of its internal drug policies even in states where the drug was legal.

"It remains unacceptable for any safety‐sensitive employee subject to drug testing under the Department of Transportation’s drug testing regulations to use marijuana," stated Jim Swart, director of the Office of Drug and Alcohol Policy and Compliance. "We want to assure the traveling public that our transportation system is the safest it can possibly be."

Voters in Washington state and Colorado approved ballot measures to legalize the recreational use of marijuana last month. The new initiatives are set to clash with federal law, which still considers the production, possession and sale of marijuana to be a crime.

Swart said the policy also applied to medical marijuana.

DOT employees such as pilots, school bus drivers, truck drivers, train engineers and others will still face suspension for testing positive for marijuana, even if they have obtained a physician's recommendation to use the drug.

Eighteen states and the District of Columbia have legalized the medical use of marijuana.

"We want to make it perfectly clear that the state initiatives will have no bearing on the Department of Transportation’s regulated drug testing program," Swart said.

The U.S. Department of Justice has been notably silent on the issue. Washington Gov. Chris Gregoire (D) and Colorado Gov. John Hickenlooper (D) have both requested legal guidance on implementing the marijuana legalization measures, but have yet to receive a response.