The corporate regulator has launched an investigation into suspicious share trading linked to the Perth airport rail project, probing the office of Western Australia's Transport Minister about a potential information leak.

Key points: Dean Nalder's office has given ASIC documents relating to a possible information leak

Dean Nalder's office has given ASIC documents relating to a possible information leak "Leak" relates to suspicious share trading in NRW Holdings

"Leak" relates to suspicious share trading in NRW Holdings NRW Holdings is preferred tenderer to build Forrestfield Airport Rail Link

NRW Holdings is preferred tenderer to build Forrestfield Airport Rail Link Government rejects calls for immediate internal inquiry

Dean Nalder has confirmed his office has handed over documents to the Australian Securities and Investment Commission (ASIC) as it examines unusual trading linked to the Forrestfield Airport Rail Link.

ASIC is investigating the possible leak of information and Mr Nalder's office is among the areas it is examining.

It has reportedly requested documents and phone records.

The share price of NRW Holdings jumped 30 per cent on February 15, three days before the announcement its joint venture had been selected as the preferred bidder for the $2 billion project.

In a response to the ASX at the time, the company said it became aware of its selection after trading closed on February 17, and requested a trading halt before the market opened the next day.

But Mr Nalder said he was confident no wrongdoing had taken place.

"There were staff that were involved from time to time in specific meetings, but all my staff were specifically excluded from anything to do with the final proponent and the prices," he told the ABC.

"My staff were only advised — and I've double and triple checked that... only became aware [of the preferred bidder], when I became aware.

"There is no accusation from ASIC or ASX that anybody, anywhere within the State Government has had any involvement in any wrongdoing."

Mr Nalder said the ASIC investigation was "due process".

"I'm quietly confident nothing will be turned up but we need to let an investigation take place," he said.

Premier Colin Barnett has previously rejected Labor's calls for a separate Government inquiry into the probity of public sector employees related to the issue, saying it would be "entirely inappropriate" because that was the role of other bodies.

Minister should have told Parliament: Opposition

Opposition transport spokesperson Rita Saffioti said the matter would be pursued in Parliament.

"This is one of the most serious matters I've seen in politics where we have a ministerial office being investigated for leaking information about a successful tenderer," she said.

"We asked the Minister about this issue in February and he denied his office knew about the awarding of the tender until just the day before.

"I think it's pretty clear that the information was leaked, so the question is where from.

"It was up to the Minister to come into the Parliament and tell us that his office and his agencies were being investigated, he hasn't and we will be asking the Minister a serious of questions today about exactly what he's known about the ASIC investigation and how many people knew about the successful bidder before it was announced."

NRW Holdings was announced as the airport rail link's preferred bidder in February. ( Supplied: Public Transport Authority )

Agriculture added to portfolio

Dean Nalder has had a short but chequered political career.

He was stripped of the finance portfolio in December 2014 after an investigation found he breached the ministerial code of conduct through his business interests and relationships.

But seen as a rising star in the Liberal Party, he retained the transport portfolio.

The Opposition has accused him of mismanagement of the portfolio after the shelving of the MAX Light Rail project and his support for a controversial underground rail tunnel for Perth's northern suburbs.

The Minister has also been heavily involved in the controversial Perth Freight Link project, which has now been put on hold for at least a year after the WA Supreme Court ruled the environmental approvals for Roe 8 were invalid.

The delays could mean the Government has to conduct a new tender process for the project, despite already selecting a preferred bidder.

Mr Nalder held onto the transport portfolio in the most recent Cabinet reshuffle, and also gained the agriculture portfolio.

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