"This is an outrageous omission.
"The 15 Auckland butchers found adding sulphur dioxide to their meat to make it appear fresher were only caught after an investigation was sparked by a local couple becoming ill from eating mince," Mr O'Connor said.
"MPI's failure to monitor this dangerous practise is made worse by its refusal to name the offending businesses. The Ministry is choosing to put the interests of these businesses ahead of consumer safety."
Labour had called for the re-establishment of a "well-resourced stand-alone food safety agency" whose job it was to protect consumers, introduce regulation and properly enforce it, Mr O'Connor said.
The illegal use of additives breaches the Food Act 1981 and could result in a fine of up to $5000 for an individual or $20,000 for a body corporate.