By Peter Hobson

CANBERRA, Oct 29 (Reuters) - Some grain handlers at GrainCorp , one of Australia's largest exporters of wheat and other crops, began industrial action on Tuesday, threatening to disrupt the harvest just as it ramps up.

Australia is one of the world's biggest shippers of agricultural products. Harvesting of wheat, barley and canola is entering full swing and will continue into January.

The Australian Workers' Union (AWU) said GrainCorp handlers in New South Wales - one of the country's biggest growing regions - would conduct impromptu hour-long strikes over the next 30 days with as little as 10 minutes warning.

"We'll be taking action at peak work periods, if a train comes in, if trucks line up," said AWU official Tony Callinan.

GrainCorp has the largest grain storage and distribution network on Australia's east coast and in some areas farmers have no nearby alternative grain handler.

Callinan said around 200 workers were taking part in the stoppages.

GrainCorp said fewer than 100 had voted in the strike ballot and it had more than 1,000 grain handlers in New South Wales including casual staff.

"Our teams are monitoring the situation and working to ensure harvest activity can continue at our sites," Jess Simons, the company's head of corporate affairs, said.

Callinan said recent pay rises were far below the rate of inflation during a period of healthy company profits and the union wants a three-year deal boosting pay by 6% in the first year, 5% in the second and 4% in the third.

GrainCorp said it had offered 6% in the first year, 5% in the second and 3% in the third.

The strikes do not yet threaten grain supply but are a headache for farmers.

"Growers are working within an extremely tight time frame and they need all hands on deck," said Justin Everitt, a grower and board member at industry group NSW Farmers.

"Strikes at receival sites will certainly come at a cost to farmers," he said.

"There will be large, random delays to when they can deliver and unload grain, which will only increase freight costs and add to the stress and fatigue of harvest."

(Reporting by Peter Hobson; Editing by Christian Schmollinger)

((peter.hobson@thomsonreuters.com;))