In one of the latest cases, a customer found a metal object in ground beef purchased at Buy-Low Foods in northeast Calgary. (CBC)

Two more cases of food tampering are under police investigation in Calgary, where seven grocery stores have now been targeted.

A customer preparing a package of ground beef purchased from the Buy-Low Foods store in the 200 block of 52nd Street N.E. found a metal object in it on Monday.

On Wednesday evening, a customer found a metal object in a pre-packaged sandwich from the Safeway in the 1400 block of 52nd Street N.E. and returned it to the store.

Neither customer was injured, said police on Thursday. They did not disclose the nature of the metal objects but said they were "similar" to push pins found in previous cases.

Grocery stores across Calgary have implemented extra security in the past several weeks after seven other cases of food tampering.

Calgary police said that they're worried about copycats.

"I think we have to balance the need to proactively notify the public when these new incidents come in with a real serious question about, are we actually maybe encouraging this type of activity? I mean there's been lots of coverage," said police spokesman Kevin Brookwell.

"That is a real … possibility now that we are having a copycat incident"

Since January, pins have been found in baked goods, cheese, juices and bulk foods four times at the Calgary Co-op in Oakridge Centre in the southwest.

A woman was charged on March 17 with mischief over $5,000 in connection with one of those food-tampering occasions.

However, since that arrest, metal objects turned up in produce and bread at three Sobeys stores and one Safeway location in the south of the city.

Police continued to urge customers inspect food purchased from grocery stores for foreign objects.

"Somebody who is really intent on doing this will likely find a way to do it. So really, the key here is I think we just have to ask the public to be vigilant. They're going to unfortunately have to check their food until this stops," said Brookwell.

He pointed out that the Criminal Code charge of mischief could escalate to one that involves injury or death if the food tampering ends up harming someone.

"The maximum sentence for that is life imprisonment so this is not a game," said Brookwell. "We're lucky so far that nobody's been hurt."

The Canadian Council of Grocery Distributors, which represents major grocery chains including those targeted, is offering a $10,000 reward for the arrest and conviction of those responsible for the food-tampering cases.