A Canadian couple is accused of importing fentanyl products from China into the United States and then mailing the powerful opioid drugs to Canada.

Karl and Sorina Morrison, both 59, were arrested at a border crossing near Niagara Falls, N.Y., last month after an investigation by U.S. authorities.

The Kitchener, Ont., couple has been charged with conspiracy to import and export controlled substances and analogues, and attempt to export controlled substances and analogues.

Each charge carries a maximum penalty of 20 years in prison and a $1-million fine.

The couple has pleaded not guilty.

In a criminal complaint filed with a New York court, a Homeland Security agent says a package mailed from China to Karl Morrison at a mailbox in a UPS store in Niagara Falls, N.Y., contained four packets, two of which were found to contain types of fentanyl.