BUENOS AIRES - Scores of grains ships sat idle outside Argentina's ports on Tuesday as the country's dockers union and port managers' chamber sparred over a strike that threatened to disrupt exports.

Agricultural powerhouse Argentina is prone to labor disputes such as the strike called by dock workers on Thursday, which propped up world soy prices until the CAPYM port chamber announced on Friday that the work stoppage had ended, only to begin again on Monday.

But union chief Omar Suarez told Reuters on Tuesday that the strike had never been called off at all, and that by Tuesday about 150 ships were forced to drop anchor and wait for the work stoppage to end before they could be moored.

This, he said, paralyzed operations in Argentina's main grains shipping hub of Rosario.

"Not one ship more will enter or leave," Suarez said. "There could be something like 150 ships halted."

The union chief added, "This is the continuation of the strike that started last week. The strike did not end on Friday. It continues in all ports."

The union, known by its Spanish acronym SOMU, has demanded that work shifts be better staffed. The disruption to port activities last week fueled a rise in Chicago Board of Trade spot soy futures.

Argentina is a top world supplier of soy and corn, and farm sector revenue is important to the government's fiscal health.

So strikes that affect exports are followed by international grains traders and sovereign bond holders alike.

A CAPYM spokesman declined on Tuesday to say how many ships were being held up by the strike, but he insisted that the dockers ended their strike late on Friday.

"The dock workers, who are represented by SOMU, worked the weekend until 5 p.m. on Monday," the spokesman said.

Argentina is the world's biggest exporter of soymeal, which is used as animal feed, and soyoil, used for cooking and in the booming biofuels sector. The Latin American country is also the No. 3 supplier of soybeans and the No. 2 corn exporter after the United States.

As global population grows to an estimated 9 billion by 2050, demand for food will nearly double, according to the United Nations. Argentina, with its vast and fertile Pampas plains, will be a key to meeting that demand.

But the country is prone to jarring labor protests. Hefty wage demands, traditionally negotiated in March and April, are common as annual inflation is reported by private economists at more than 20 percent per year, one of the world's highest rates.

Some unions have close ties to the government of Cristina Fernandez, who was elected to a second term as president last year despite regular spats with farmers and orthodox economists who say her state-centric policies scare off investment.