Brambles spin-off Recall Holdings has received a big takeover bid from US logistics giant Iron Mountain.

The two companies have signed a scheme implementation deed for the merger, which will see Iron Mountain acquire Recall in a deal valuing the Australian-listed company at $A3.4 billion.

Recall shareholders have two options: they can get a cash payment of 50 US cents (65 Australian cents) plus 0.1722 Iron Mountain shares for every share they hold; or they can opt to receive an $A8.50 cash payment from a $A225 million pool provided by Iron Mountain, which was announced in April.

The new deal comes after Iron Mountain's share price slid down, lowering the paper value of the merger from Recall’s perspective.

Iron Mountain chief executive William Meaney said the company made an extra 50 US cent per share offer because it realised the deal would be even more beneficial than originally forecast.

“It's much more related to the transaction of putting the two companies together, there was additional benefit that we found,” Mr Meaney said.

Iron Mountain says the merger should result in $US155 million in net synergies, an increase on the $US125 million to $US140 million first forecast.

The deal will leave Recall shareholders owning 21 per cent of Iron Mountain, which is set to establish a secondary listing on the Australian stock market.

The takeover deal is subject to regulatory approvals and is expected to be completed in early 2016.

Recall chief executive Doug Pertz has welcomed the deal

“With the significant synergies and accretion generated by the combination, we believe the potential value creation for both sets of shareholders will be considerable,” he said.