Someone has tampered with food for a second time at the Calgary Co-op store at Oakridge Centre. (CBC)

Calgary police say they are closing in on suspects after a grocery store that found some of its products had been sabotaged with steel pins last month was again forced to close after further product tampering.

Police said the tampering seems designed to disrupt business rather than harm customers.

Calgary Co-op reopened its Oakridge Centre on Southland Drive and 24th Street S.W. on Thursday after closing Wednesday night after staff again found evidence of product tampering.

"We have a number of suspects right now and we are just going to narrow that down through a number of investigative strategies," said Calgary police Staff Sgt. Don Coleman.

Coleman would not say if the suspects were store employees but he said it appears obvious the latest tampering incident is related to an occurrence in January.

As with the previous incident, when Co-op staff found steel pins in bakery goods, police were immediately notified and are conducting a criminal investigation.

"Obviously this is very alarming to consumers, very alarming to our employees," said Co-op spokeswoman Sara Boutron, adding the store is co-operating fully with police. "Calgary Co-op is doing its due diligence to try and find out who did this."

The store reopened Thursday morning after a thorough sweep by staff found no more product tampering. On Wednesday, staff found "metal items" similar to those found in the January incident, this time in garden produce, including carrots.

Boutron said staff believe no tampered goods left the store.

"Calgary Co-op's top priority is customer safety and it is continuing to take this matter very seriously," said Boutron, adding the grocer is asking customers who recently purchased items from the Oakridge Centre to be diligent in checking for tampering.

The grocer did not receive any threats, and the company doesn't know why anyone would tamper with food. There have been no reports of injuries or of problems at other Calgary Co-op stores.

Customers who are unsure about a product may return it to the centre for a full refund.