Although the legalization of both medical and recreational use of marijuana continues to grow at the state level, the U.S. Postal Service has cautioned that ads promoting the drug or a dispensary that appear in a publication sent through the mail may violate federal law.

In late November, the Portland, OR, district of the USPS sent a memorandum to newspapers and periodicals in the Northwest region stating that mail pieces containing advertisements about marijuana are "nonmailable." The agency's Domestic Mail Manual restricts "any advertising, promotional, or sales matter that solicits or induces the mailing of any article described as hazardous, restricted, or perishable." Marijuana is classified as a Schedule I controlled substance under federal law, making it restricted.

Therefore, both the mailing of marijuana and the mailing of an advertisement that "advocates the purchase of clinical marijuana through a Medical Marijuana Dispensary" are unlawful, the Service wrote.

When multiple newspapers made the memo public, Oregon lawmakers responded with their own missive to the Postmaster General, requesting "a detailed explanation" of the Postal Service's policy.

"Small businesses and community newspapers rely on advertising to be successful," Sens. Jeff Merkley and Ron Wyden and Reps. Earl Blumenauer and Suzanne Bonamici wrote, noting that four states (including Oregon) have legalized the adult use and sale of marijuana, with 23 states, the District of Columbia, and Guam permitting full medical marijuana programs and an additional 17 states authorizing more limited medical marijuana programs.

"What is the specific statutory authority that gives the USPS the ability to restrict the types of advertising that newspapers or periodicals that are mailed contain," the legislators asked, also wondering if the policy laid out in the memo is applied across the country or if individual districts create their own policies. "What discretion does a regional postmaster have in enforcing or implementing these policies, specifically in states where marijuana is legal?"

The lawmakers also queried how the policy would be enforced. Pursuant to a provision in the federal government spending bill, the Department of Justice is currently barred from spending any funds to prevent medical marijuana states from implementing their own state laws with regard to such programs. "Therefore, [the Drug Enforcement Administration] would arguably not be able to enforce policies regarding the in-state mailing of advertisements for state-legal medical marijuana products. If this is a policy with legal effect in all 50 states, then why is the USPS helping to uphold laws in medical marijuana states that cannot be enforced by the DEA per the appropriations language? Did the USPS cooperate with anyone at DEA or DOJ in establishing this policy?" the legislators wrote.

To read the Postal Service memorandum, click here.

To read the letter from lawmakers to the Postmaster General, click here.

Why it matters: As the number of states legalizing recreational and/or medical marijuana use continues to grow, problems have increasingly arisen with regard to the application of federal law. The issue recently made headlines in the context of broadcast advertisements when a commercial for a Colorado dispensary was pulled at the last minute after the network elected to play it safe and avoid any potential violation of federal law.