Printing of same-sex marriage survey forms is under way despite a chance the High Court could stop it.
The court is hearing a challenge to the survey launched by marriage equality advocates, which could come down with a finding as early as Wednesday.
Finance Minister Mathias Cormann confirmed on Tuesday printing of the forms had begun.
"Because the printing and drying of the survey forms, instruction letters and envelopes takes some time, printing is currently under way," he said.
However the government had given a commitment not to mail the forms until the court determined the case.
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It's expected $8 million will have been spent on advertising production and placement by the time of the court decision.
Other costs related to updating the electoral roll, operating the information line, establishing IT and security protection, survey operations, and materials printing have not yet been finalised.
Contracts include clauses for termination and reduction for convenience.
Senator Cormann said the ABS had taken steps to ensure "only necessary expenditure" is undertaken prior to the High Court decision in order to deliver the survey within the required timeframe.
The forms are due to be mailed from September 12.
