The U.S. Postal Service has warned newspapers that it is a felony to mail material that includes marijuana advertising.

The Oregon Newspaper Publishers Association forwarded the recent federal advisory to its 100 or so members this week.

CHICAGO (WLS) -- Since recreational use of the marijuana became legal in several states, authorities report a major jump in the number of pot-filled packages being sent through the mail.

Newspapers in half the states are breaking the law if they mail publications containing ads for marijuana products — even though the states have legalized pot, the U.S. Postal Service said last week.