A US federal court ruled the Bush administration cannot relax 'dolphin-safe' labeling laws for cans of tuna.
The US commerce department attempted to ease the 1990 standards passed by Congress to meet the demands of Mexican and South American fishing industries.
The dispute centres on the use of huge 'purse seine' nets which snare dolphins along with tuna swimming underneath them.
The new rule would allow the 'dolphin-safe' label for tuna caught with those kinds of nets if observers on the foreign boats had not seen dolphins killed or seriously injured.
The 9th US Circuit Court of Appeals, well-known for its liberal rulings, called the government's efforts 'arbitrary', 'capricious' and political influenced.
'This evidence shows that the decision-making process... was influenced to at least some degree by foreign policy considerations rather than science alone', wrote Chief Judge Mary Schroeder.
The court added that fishing practices such as 'purse seine' have killed more than six million dolphins.
