Prime Minister Scott Morrison promised during the election campaign a Coalition government would go guarantor for up to 10,000 first-home buyers a year who had already saved up at least 5 per cent of a deposit. This would help them avoid paying lenders mortgage insurance, which is typically charged to borrowers who have less than 20 per cent of a deposit.

A Senate committee has heard concerns that not enough is known about the details of the plan, as the legislation leaves that to an Investment Mandate that is yet to be published. The Scrutiny of Bills committee said it was "particularly concerned" that details were left to non-disallowable delegated legislation and "therefore will not be subject to effective parliamentary oversight".

Assistant Treasurer Michael Sukkar said the details of the program, like how many people were eligible and what loans would be covered, needed to be in the Investment Mandate to ensure the scheme could be responsive to the market. He also pointed out the Investment Mandate allowed further consultation to take place before the scheme starts on January 1.

The scrutiny committee disputed the minister's points and told the senators of its concerns.

Labor senators expressed concern the Investment Mandate hadn't been finalised and said more detail would have been preferred, but didn't dissent from the majority report recommending that the bill be passed.