Firms in Sweden have sold about 200 tonnes of Baltic salmon in Europe despite an EU ban targeting toxic chemicals in fish, officials say.
The ban does not apply to Baltic salmon sold to domestic consumers in Sweden, Finland and Latvia. But the sellers are required to give advice about safe limits for consumption, set by the EU.
Dioxins found in Baltic herring and salmon prompted the EU ban in 2002.
A French firm imported 103 tonnes of Swedish salmon, but no longer does so.
Pecheries Nordiques told the AFP news agency that its tests had found no problems with the fish, imported in 2011 and 2012. "Nobody told us it was illegal," chief executive Francois Agussol said.
Jan Sjoegren of Sweden's National Food Agency told the BBC that Baltic salmon had also been exported illegally to Denmark and the Netherlands from Sweden.
The agency has alerted the European Commission, which deals with national food safety authorities.
A firm in Karlskrona has been reported to the Swedish customs authorities over the salmon exports, and a firm in Hammaroe is also being investigated, Mr Sjoegren said.
The latest alert about Baltic salmon exports follows a horsemeat contamination scandal in the EU which affected many countries.
"We don't think more salmon is being exported now, but because of the horsemeat scandal we are stepping up action on food fraud," Mr Sjoegren said.
Sweden's National Food Agency says the average intake of dioxins among adult Swedes is well below the "tolerable weekly intake" set by the EU.
Children and young women, it adds, should especially limit their consumption of wild Baltic fish because dioxins pose the most risk to babies and young children.
Dioxins spread by incineration and chemical pollution can accumulate in the body over years and can trigger cancer or reproductive abnormalities.
The European Food Safety Authority says that, on average, Baltic herring and wild Baltic salmon are respectively 3.5 and five times more contaminated with dioxins than non-Baltic herring and farmed salmon.