The U.S. Postal Service has issued a national policy declaring it illegal to mail newspapers with marijuana advertising but instructing local postmasters to continue to accept the mail.

The guidance, issued after the Postal Service in Portland raised questions in late November about marijuana ads in the Coast Weekend section of the Chinook Observer, places the legal burden on newspapers to decide whether to risk the mailings.

Local postmasters are not authorized to determine whether the mailers are illegal or to reject the mail. The policy instructs postmasters to advise newspapers of the federal law that classifies marijuana as an illegal drug and to report the mailers to the U.S. Postal Inspection Service for potential referral to federal law enforcement agencies.

The national policy was outlined Tuesday in a letter from Thomas Marshall, the general counsel and executive vice president of the Postal Service, to U.S. Sen. Ron Wyden, D-Oregon, who along with other Oregon lawmakers had sought clarification on behalf of EO Media Group, which publishes the Chinook Observer, The Daily Astorian and other newspapers.

“Based on our review of the pertinent statutory provisions, we have concluded that advertisements for the sale of marijuana are non-mailable,” wrote Marshall, who advised Wyden that it would be up to Congress to change federal law and allow the ads to be “freely distributed through the U.S. mail.”

“We are working as a delegation to quickly find the best option to address this agency’s intransigence,” Wyden said in a statement Thursday with U.S. Sen. Jeff Merkley, U.S. Rep. Suzanne Bonamici and U.S. Rep. Earl Blumenauer. “We want federal authorities to respect decisions made by law-abiding Oregonians and small business owners in the state.

“Unfortunately, the outdated federal approach to marijuana as described in the response from the Postal Service undermines and threatens news publications that choose to accept advertising from legal marijuana businesses in Oregon and other states where voters also have freely decided to legalize marijuana.”

The national policy creates a potential conflict between the emerging marijuana industry in Oregon and other states and the federal government. Oregon, Washington state, Alaska and Colorado have legalized marijuana for recreational use, but the federal government considers marijuana a Schedule I drug similar to heroin and methamphetamine.

The Postal Service maintains that federal law prohibits ads for Schedule I drugs and the use of the mail for “the commission of any act or acts constituting a felony.”

“These provisions express Congress’s judgment that the mail should not be used as a means of transmitting advertisements for the sale of marijuana, even if that sale is allowed under state law,” Marshall wrote. “We believe that we have clear statutory authority to regulate the mail in a way that effectuates Congress’s intent in this regard.”

Under the Obama administration, the U.S. Department of Justice has indicated that possession of small amounts of marijuana for recreational use would not be a federal enforcement priority.

Yet the Postal Service’s policy puts newspapers and others that advertise marijuana through the mail under a legal cloud.

Coast Weekend, which is inserted into the Chinook Observer and The Daily Astorian, accepts advertising from marijuana shops in Washington state and medical marijuana dispensaries in Oregon that are temporarily allowed to sell recreational marijuana under state law.

Roughly half of the weekly Chinook Observer newspapers are distributed by mail, while only a small portion of Daily Astorian newspapers are sent by mail.

Matt Winters, the publisher of the in Long Beach, said the notification from the Postal Service in November was a surprise because recreational marijuana has been legal in Washington for three years and the publication has been running marijuana ads for months without complaints. Recreational marijuana became legal in Oregon this year.

EO Media Group will have to decide soon whether to continue to publish and mail newspapers with the ads.

“We’re in touch with our legal counsel and we’re looking at our options,” said Steve Forrester, the editor and publisher of The Daily Astorian and the president and CEO of EO Media Group.