See the following link for a Lexology article - it is very informative. Call KCG about reviewing your policy to make sure you are properly equipped to handle issues as they might arise.
The U.S. Department of Justice announced an update to its federal marijuana enforcement policy in light of recent state ballot initiatives (Colorado and Washington) that legalize, under state law, the possession of small amounts of marijuana and provide for the regulation of marijuana production, processing, and sale. See this link for the actual article.
Bottom line - marijuana is still a Schedule I drug, regardless of state laws, and is prohibited for those covered under the Department of Transportation Federal regulations.