The case resulted from a routine inspection
Portadown bakery Irwin's has been fined £1,500 for selling underweight bread.
It follows an inspection from the Trading Standards Service which found that 38 out of 51 loaves from two lines contained less than the marked weight.
Inspectors found no checks had been made to ensure the weights of the particular products were correct.
Irwin's said they were making a new bread which "unfortunately incurred more weight loss than was expected" during the baking process.
"We take this incident extremely seriously and would like to reassure consumers that we have taken rigorous steps to ensure this problem does not occur again," said Michael Murphy, Irwin's commercial controller.
"We have increased the weight of ingredients for the specific products, which will, in fact, mean that they will now exceed the required product weight."
Trading Standards inspector Bill Malloy said consumers were entitled to expect that the bread they buy weighs what is stated on the packaging.
"Bakeries have an obligation to ensure that the weight of loaves meets the minimum weight standards laid down, and should have measures in place to check this," he said.
"With the increasing price of many foods, it is more important than ever that consumers are sold the amount stated on the packaging of products."