A spokesperson for the Co-op said two of the chocolate figures had been found to contain a small button-cell battery.
"The health and safety of our customers is our top priority," said the spokesperson, adding that the Co-op was investigating and the police and Food Standards Agency were being notified.
No other products are affected.
The Co-op chocolates that had been subject to tampering were bought at two locations, one in Suffolk and one in Essex.
It is thought that the tampering took place after the Santas left the factory.
Surgeons recently warned that button batteries pose a potentially deadly risk to young children.
If accidentally swallowed, the small, round batteries can get lodged in the oesophagus and burn a hole through its lining.
The most serious cases are associated with Lithium button batteries larger than 20mm (the size of a 10 pence piece) which can cause severe injury within two hours.
London's Great Ormond Street Hospital said in September that it had seen a big increase in cases in the past year.
The Co-op said customers with one of these products should not eat it, but call the company's customer relations team for a full refund.
Anyone who is concerned should call Freephone 0800 0686 727.
The Co-op grocery chain has announced a nationwide recall of 165,000 hollow milk chocolate Santa figures after two alleged tampering incidents.