Brambles Ltd's boss Mike Ihlein has stepped in to quell a $2.5 billion run on his company's stock, fueled by concerns that the world's biggest pallet supplier had been dumped by US retail giant Wal-Mart.

Mr Ihlein said there had been a "dramatic over-reaction" to news that its major US customer, Wal-Mart, was reviewing its pallet arrangements with the logistics firm.

Brambles shares fell almost 18 per cent - to a low of $8.25 after closing at $10.03 - in morning trading due to uncertainty about the financial impact of the announcement.

At its worst, the investor rout stripped almost $2.5 billion from the market value of the logistics giant.

But Mr Ihlein's intervention appeared to put a floor under the shares and Brambles clawed back some of its losses to end $1.03, or 10.27 per cent, lower at $9.00.

Even so, the drama still stripped $1.44 billion from the company's worth by the close of the session.

The panic began when Brambles announced Wal-Mart was reviewing its pallet arrangements, currently handled by Brambles-owned CHEP.

Wal-Mart had indicated it may contract a third party or begin doing the job itself, Brambles said.

As the rout continued Mr Ihlein rushed out a statement clarifying that CHEP's sales revenue is generated from manufacturers and suppliers in connection with deliveries to retailers, such as Wal-Mart.

"CHEP does not generate sales revenue from Wal-Mart itself," he said.

"The discussions with Wal-Mart have no impact on CHEP's issue volumes or sales revenue."

Mr Ihlein described the pallet management service provided to Wal-Mart as "cost neutral" to CHEP.

In a hastily-arranged briefing in the afternoon, the Brambles boss said the initial announcement was put out to ensure "all of the market had the same level of knowledge that clearly some people outside of our company became aware of yesterday".

"Secondly, Wal-Mart is an important customer for us," he said.

"As we work through the alternatives with Wal-Mart, we'll consider all possible things that will deliver them the best outcome and for us and the manufacturers.

"When we come to a resolution on all of that, in due course we'll make an announcement to the market."

But Mr Ihlein resisted probing by analysts about whether CHEP was a candidate to become a "third-party" pallet manager under Wal-Mart's revised arrangements.

"We can't comment on our discussions with Wal-Mart," Mr Ihlein said.

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.

There are around five to 10 million CHEP pallets in Wal-Mart's distribution network at any one time, from a total of 76 million CHEP pallets in the US.

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

The group had 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.