BUENOS AIRES- Activity in some grain ports in Argentina, a leading global food supplier, was halted on Tuesday by a strike over wages, two labor organizations said.

The Urgara group representing grain inspectors and the Argentine Federation of Oilseed Workers went on strike Tuesday morning, after weeks of talks failed to yield a contract.

The strike affects a few ports in the towns of San Lorenzo and Timbues and the city of Puerto General San Martin, which together form the northern part of Argentina's main grains hub of Rosario, on the Parana River in Santa Fe province. About 80% of the country's grains exports come by way of Rosario.

The CIARA-CEC chamber of export companies said on Monday that the workers were demanding excessive pay increases.

Juan Carlos Peralta, press secretary for Urgara said cargo ships were also stalled in Quequen and Bahia Blanca, further south in the province of Buenos Aires, with activity in both ports "paralyzed".

A spokesman for the federation said participation by workers in the strike was "practically total" in many Argentine oilseed crushing plants, which manufacture soymeal livestock feed used to fatten poultry and hogs from Europe to Southeast Asia.

Argentina is the world's top exporter of the feed as well as a major soybean, wheat and corn supplier. December is not high export season in Argentina, where this year's wheat harvest is just getting started and corn and soy are still being planted.

(Reporting by Maximilian Heath; Writing by Hugh Bronstein; Editing by Alexander Smith) ((hugh.bronstein@thomsonreuters.com; 5411 4318 0655; Reuters Messaging: hugh.bronstein.thomsonreuters.com@reuters.net))