The "Banana wars" began in the 1990s
European Union import duties on bananas flout global trade rules, the World Trade Organization (WTO) has ruled.
The WTO case was brought by Ecuador, which, along with other Latin American countries, claims the EU favours Caribbean and African producers.
The EU said it was considering appealing against the ruling.
The ruling is the latest in a series of WTO decisions against the EU's banana regime - the longest running dispute in WTO history.
If the ruling is upheld, Ecuador will be able to impose trade sanctions on the EU.
"It's a big victory for us," said Cesar Montano Huerta, from Ecuador's WTO mission.
"But we are still hoping to come out with a solution and negotiations for this issue."
Ecuador, the world's biggest banana exporter, first brought the case in 1996 with Guatemala, Honduras, Mexico and the US.
Colombia, Nicaragua and Panama have also joined the dispute.
The US does not export bananas to the EU but three large US-based multinationals, including Chiquita, have plantations in the region.
The EU has been accused of giving preferential treatment to its members' ex-colonies in Africa, the Caribbean and the Pacific region.
EU officials have been working furiously to hammer out new trade deals with about 80 countries in Africa, the Caribbean and the Pacific (ACP) to end special trade relationships that have been in place since the 1950s.
These allowed a range of products, including banana crops from ACP states, to enter the EU with no duty to pay, while Latin America exports were charged.