The supermarket is recalling its 45p Sainsbury's Wholemeal Bread Medium Sliced and Thick Sliced loaves because they may contain small pieces of metal.
The Food Standards Agency (FSA) said the presence of metal pieces makes the bread unsafe to eat and presents a risk to health.
The 800g loaves have January 19, as the 'best before' date. No other Sainsbury's products are known to be affected.
A Sainsbury's spokesman said: "We have been made aware of the possible presence of tiny metal pieces in a small number of the above products.
"As a precautionary measure, we are asking customers who have purchased this product with the best before date, to return it to their nearest Sainsbury's store, where they will receive a full refund.
"No other products or date codes are affected by this issue, and we apologise for the inconvenience this may cause."