The Marine Stewardship Council (MSC) has suspended the sustainability certification of North Sea cod after stocks dropped below a safe biological level.
The MSC said the cause of the decline is unclear, but scientists have suggested it could have been affected by warming sea temperatures and fewer young fish surviving to adulthood.
Erin Priddle, UK and Ireland programme director for the MSC, said: "The decline in the North Sea cod stock is a worrying development, with the latest stock models suggesting that the fishery has not recovered as well as previously thought."
He added: "While this news is devastating for industry, it is a testament to the MSC Standard working as it should: to pick up on threats to stock sustainability, as is the case with North Sea cod. It is imperative that industry works collaboratively with fishery managers, NGOs and the wider seafood supply chain to introduce effective measures that will see this fishery once again achieve certification."
The Scottish fishing industry has committed to a five-year project to return the stock to health.
Mike Park, Chairman of the Scottish Fisheries Sustainable Accreditation Group, said: "The industry are concerned that notwithstanding their best efforts to continue to rebuild North Sea cod some developments are taking place that seem beyond their control.
"That said, they are committed to introducing balanced and proportionate measures in an attempt to reverse the decline. We will be liaising closely with managers to ensure that these measures apply to all vessels operating within the mixed demersal fishery."