Cargo backups due to a labor dispute at West Coast container ports are pushing down corn prices in Illinois and could cause importers to renege on deals, adding to record domestic stockpiles of the grain.

With container shipment delays of two months or more at ports in California, grains handlers that transport supplies to the ports are slowing operations in the fastest-growing segment of agriculture exports.

Corn buyers south of Chicago, where railroads converge in the country's busiest rail hub, are slashing their bids.

The DeLong Company, one of the biggest shippers of "containerized" grain to destinations in Asia, is canceling a loading shift that was scheduled for Saturday in Minooka, Illinois. The company also reduced what it was willing to pay for corn by 7 cents, to $3.52 per bushel.

"It's really affecting our bid. We can't ship the stuff. If we can't ship it, we can't bid for it," said DeLong grain buyer Kent Hamm.

A labor deal at 29 ports on the West Coast moved closer this week but it will take months to shift the backlog at ports in Los Angeles and Long Beach.

Containers loaded outside Chicago normally are hoisted onto an ocean vessel on the West Coast within 10 days to two weeks, said Jay O'Neil, senior agriculture economist at Kansas State University.

"Instead, they're taking two months. That's problematic for shippers," he said. "(Buyers) could argue to back out of their contracts. They could try to hold the shippers' feet to the fire, so to speak, to cancel or renegotiate," he said.

Canceled deals would add to record domestic stockpiles for farmers already facing the lowest corn prices in more than four years.

The container business for grain and soybeans is still tiny, accounting for only about 5 percent of U.S. agricultural exports. But containers are smaller and more easily tracked than bulk vessels, raising their popularity as buyers increasingly demand non-genetically modified soybeans or corn.

A container generally can hold about 20 tonnes of agriculture goods. Bulk Panamax vessels, which account for the vast majority of U.S. grain exports, can hold 60,000 tonnes.

The United States imports goods such as electronics and clothing from Asia in containers that are then reloaded with paper pulp, scrap metal, food-grade soybeans, corn or distillers' dried grains to return - or "backhaul" - primarily to China, Taiwan and Indonesia.

(Reporting by Michael Hirtzer; Editing by Dan Grebler)