The Turnbull government is looking at ways to hold the same-sex marriage postal survey even if the High Court declares it has been unlawfully funded, an inquiry has heard.

The head of the Australian Bureau of Statistics, David Kalisch, said the ABS and Mathias Cormann's Finance Department had begun contingency planning last week.

"We have looked at some of the dimensions and have had early discussions with our colleagues across government, but they're matters for [the] government," he said Thursday morning.

"We have given thought to what some of the funding options and opportunities might be. We've had some conversations with other parties across government ... primarily the Department of Finance."