Border officers were suspicious when they opened a suitcase at the Calgary International Airport earlier this month and discovered it contained tennis balls.

They noted several "anomalies" in the Sept. 7 discovery.

Underneath the felt exterior was a layer of masking tape — an indication the sporting goods had been tampered with.

Further investigation showed they contained a black, tar-like substance.

Tennis balls found in a suitcase at the Calgary airport on Sept. 7 were examined after it appeared they had been tampered with. (Canada Border Services Agency)

It tested positive for suspected opium, the Canada Border Services Agency said in a release Wednesday.

Officers seized 3.3 kilograms of suspected opium concealed inside the tennis balls. They also seized a small amount of steroids.

The traveller was arrested and turned over to the RCMP along with the seized drugs.