A Liberal-National Party senator has updated his register of interests following questions about his links to a company with government contracts.
Under section 44 of the constitution, anyone who holds "any direct or indirect pecuniary interest in any agreement with the public service of the commonwealth" is disqualified from running for parliament.
Queensland senator Barry O'Sullivan has deleted a reference to "Newlands Civil Construction" on the public register, which was previously noted as being a subsidiary of O'Sullivan and Sons.
The deletion is backdated to June 16 - the date on which the federal and Queensland governments jointly announced disaster assistance following the March floods in north Queensland.
The register of interests shows Senator O'Sullivan owns a portion of a company called Jilbridge Pty Ltd.
Jilbridge has a share of O'Sullivan and Sons Pty Ltd, which - until the change on the register - was a shareholder in Newlands Civil Construction, a company managed by the senator's son.
Labor has asked questions about Newlands having been awarded contracts valued at more than $2 million under the government's natural disaster relief and recovery arrangements.
Last week in parliament, Attorney-General George Brandis said he had "no reason to believe" Senator O'Sullivan's business dealings were not appropriate.
Labor senator Anthony Chisholm said it was "very concerning" Senator O'Sullivan had rushed to amend and backdate his register of interests.
"Despite George Brandis saying he has no reason to look into Senator O'Sullivan's interests, something doesn't smell right," Senator Chisholm said.
"This is a very serious matter that the government can't just brush off. Senator O' Sullivan needs to come clean and address these accusations."
In August it emerged Newlands also has a four-project contract with Nexus Infrastructure - one of the partners on the Toowoomba Second Range Crossing, a $1.6 billion road bypass.
The federal government is contributing $1.14 billion, or 80 per cent of the project cost, and the Queensland government's share is 20 per cent through a public-private partnership contract.
It is understood the federal funding is combined with state money under the Queensland Transport and Roads Investment Program, and the Queensland government makes payments to Nexus under the PPP contract.
Comment was being sought from Senator O'Sullivan's office.
By Paul Osborne