In the latest integrity issue to hit Leighton Holdings - which owns Thiess - Fairfax Media has found that Thiess has paid Indonesian security officials tens of thousands of dollars.

Fairfax has confirmed that Thiess deposited a large sum in the bank account of a relative of a senior Indonesian security official, while other payments were made in cash.

In return, it is believed these officials directed forces under their command to provide security at Thiess' coalmines in South and East Kalimantan, where there has been union unrest and accusations of police brutality.

Australian law prohibits giving a foreign official a benefit to secure a business advantage that is not legitimately due.

Well-placed sources said the company had referred the matter to law firm Allens for advice on whether federal police should be notified.

Fairfax has also obtained - and today published online - a confidential 2007 agreement between Leighton Holdings and two wealthy Middle Eastern businessmen in connection with a merger to create the Dubai developer Habtoor Leighton Group, which has struggled to make a profit since its inception.

The documents show that despite Leighton's $343 million investment in HLG in 2007 - and a later decision to prop up the ailing firm with large interest-free loans - the merger involved Leighton giving significant management and board control to Riad Al Sadik and Mohammad Al Habtoor.

The confidential agreement states that key HLG board resolutions "shall not be valid" unless backed by "a number of partners representing at least 75 per cent of the company". This appears to ensure that even if Leighton Holdings, which controls 45 per cent of HLG, bought out Mr Sadik or Mr Habtoor - who each control 27.5 per cent - Leighton would still fall short of the numbers needed to carry a vote.

A former company executive said: "If you are not going to get control of a company when you become a significant investor, you have to do very good due diligence to ensure your investment will be protected by those that have control. We know that this due diligence wasn't done and the merger has been a financial disaster."

Thiess Indonesia's connections with military and police officials came to public attention in Indonesia in March 2012 when workers at the company's East Kalimantan mine began to protest.

Indonesia's mining union told Fairfax that workers were met by police and military officers with batons.

It is possible that the payments made by Thiess to security officials would not breach Australian law on the basis that the firm was entitled to the security provided and it did not amount to a "business advantage".

However, the relative size of the payments and the fact that they may have gone to third parties, rather than the officers who provided on-the-ground security, raise the possibility that the money was simply pocketed as bribes.

A spokeswoman for Leighton Holdings said the company would not comment on the HLG dealings because they were "the subject of commercial and confidential arrangements".

In response to the Indonesian allegations, she said: "We do not comment on matters that are the subject of old and unsubstantiated media reports or speculate on their implications."