INVESTORS have begun bailing out of Brambles Ltd after it announced a major US customer, Wal-Mart, was reviewing its pallet arrangements with the logistics firm.

Brambles shares had slumped $1.46 cents, or 14.56 per cent, to $8.57 by 11:30am amid uncertainty over the financial impact of the announcement.

Brambles said Wal-Mart was changing its handling of pallets, including its arrangements with Brambles' pallet and container business CHEP, and other pallet pooling companies.

But the Australian logistics company did not give details of whether the decision would have any financial impact.

CHEP is owned by Brambles and currently manages the picking up and sorting of pallets, used to move goods, at many Wal-Mart facilities in the US.

Shaw Stockbroking analyst Brent Mitchell said it was difficult to quantify the revenue and profit at risk through CHEP's Wal-Mart contracts.

"That information is not available, so it's a bit hard to put figures on it," Mr Mitchell said.

He speculated that Wal-Mart contributed no more than five per cent to CHEP's US profit.

"It doesn't appear that all the businesses are at risk. You'd have to expect the Wal-Mart business to be at the low end in terms of the margin range."

Nevertheless, investors were responding to the uncertainty of how the announcement might affect Brambles outlook.

"The uncertainty that it has created has caused that reaction," Mr Mitchell said.

Brambles said Wal-Mart had indicated it may contract directly with third party pallet management service providers to retrieve and sort pallets at its own facilities in the US, or provide the services itself.

The company said it was working with Wal-Mart to identify ways in which CHEP could continue to supply low-cost services to Wal-Mart and its supply chain.

"Brambles and CHEP strongly value the relationship with Wal-Mart and will continue to work with Wal-Mart to develop the optimal supply chain solution for this important customer," it said in a statement.

Brambles was bullish in its outlook at its first half results in February, with plans to expand CHEP into India.

The company booked a first-half net profit from continuing operations of $US296.7 million ($A323.5 million), which was up 10 per cent, or three per cent in constant currency terms.

CHEP sales increased 12 per cent to $US1.75 billion ($A1.91 billion) in the half year, led higher by CHEP Americas, where sales rose 11 per cent on strong demand for grocery products.