Fishermen have blockaded several Mediterranean ports against cargo and passenger ships as part of their protest for government help to offset record high fuel costs.
The protest follows a similar strike by truck companies earlier this month, which ended after the government agreed to some concessions on fuel costs.
Delays at ports are costly for those who charter ships as they have to pay so-called demurrage charges if the vessels are still at sea when their contract expires.
"This is a complete pain ... the impact is financial, there are delays, ships are waiting in ports and that costs money," a Madrid-based grains trader said.
Twenty-seven ships, carrying oil, cars and grain, were waiting outside Tarragona on Wednesday, a spokesman there said. A port source said one of those ships was carrying 20,000 tonnes of rye and triticale from Germany and Poland and another was carrying 50,000 tonnes of Canadian wheat and peas.
Further south in Cartagena, nine ships were waiting to unload, the port's website showed. Two carried grain from Poland and France, one had 24,300 tonnes of Brazilian soyameal, and two carried oil, the website showed.
"This is messing things up ... it affects the whole country apart from the north," another Madrid grains dealer said.