Specifically, we're talking salmon caught in the Baltic Sea. The EU banned the export of Baltic salmon from Sweden back in 2002 due to the fact that they were found to be heavily contaminated with dioxins.
But that didn’t stop Swedish firms from selling 200 tons of the fish to companies in France, Denmark and the Netherlands.
A French firm that bought 103 tons of the Baltic salmon in 2011 and 2012 said they did their own tests which did not reveal dioxins in the fish.
"Nobody told us it was illegal," chief executive Francois Agussol told AFP.
One Swedish firm has been reported to Swedish customs for breaching the ban, and another is under investigation, Jan Sjoegren of Sweden's National Food Agency told the BBC.
Domestic sales of the salmon in Sweden, Finland and Latvia were exempt from the ban, but even in those countries, sales must adhere to guidelines regarding safe limits of consumption.
Dioxins are generally released as industrial byproducts. They can cause cancer, developmental and reproductive problems, among other issues, according to the World Health Organization.
The Swedish National Food Agency recommends consumption of Baltic Sea salmon and herring no more than once a week. Children and babies are most vulnerable to dioxins, so for those under 18 and women of childbearing age, the limit is much lower, about two to three times a year.
Demand, however, is also low; the average adult in Sweden does not exceed those limits, the agency estimates.