A spokesman for Fair Work Australia said yesterday that the investigation into Mr Thomson and the Health Service Union's finances might not be publicly released.

Since 2009, Fair Work Australia has been examining allegations of financial irregularities at the union formerly headed by Mr Thomson, now the MP for the New South Wales seat of Dobell.

It's been claimed Mr Thomson used union credit cards for prostitutes, lavish meals and cash withdrawals - claims he denies.

The backbencher's vote is crucial to the survival of the Gillard minority government.

Opposition frontbencher Scott Morrison said there was ``a real stench'' surrounding the government on the issue.

``It is very hard for the Australian people to have any confidence in a process which is clearly being delayed by extensive periods of time,'' Mr Morrison said yesterday.

``There is a very real perception out there that if this matter is not concluded properly, then this government has to answer questions about what are they seeking to cover up.''