Maybe it’s time to zero out your marijuana business’s marketing and advertising budget.

The U.S. Postal Service has issued a statement saying that it’s illegal to mail material with marijuana advertising, even in those states that have legalized marijuana. The USPS cited the federal Controlled Substances Act as the legal underpinning for its decision, according to Thomas Marshall, the Postal Service’s general counsel.

Additionally, it’s illegal to use the U.S. Mail to facilitate any act that constitutes a felony, Marshall said.

The Post Office took the step of issuing the statement, after Democratic members of Oregon’s congressional delegaton asked Postmster General Megan Brennan for a more “detailed explanation” of its policy. The delegation’s action followed a warning sent by the Oregon Newspaper Publishers Association to its members, urging them to reject any advertising related to marijuana. Many newspapers are circulated through the U.S. Mail.

The Postal Service took the additional step of issuing a national policy that essentially reiterates the general counsel’s interpretation; the policy was issued as a result of the newspaper association’s concerns.

But there is a potential loophole to the new Post Office regulation, at least based on how Marshall reads the law. Local postal officials can not refuse to accept mail that violates federal policy, including marijuana-related ads.

That’s because local postal officials lack the legal authority to make a determination on their own about whether a parcel is mailable or non-mailable. Furthermore, local postal officials cannot deny matter from circulating through the mail, even if it contains marijuana advertising. Instead, the local-level postal official should forward mail containing potentially illegal advertising to higher-up authorities.

With that in mind, should marijuana entrepreneurs feel safe to send marketing materials through the mail? Some publications in the Portland, Ore., area have been publishing ads from marijuana-related businesses for years.

The Democratic members of Congress from Oregon issued a joint statement, in which they said the legal interpretation from the Post Office’s Marshall is outdated and uncompromising, and that decisions made by Oregonians that are legal should be respected as such.

It appears, then, that the issue of marijuana ads has a long way to go before it’s reached a clear-cut conclusion.