Labor queries govt's pre-election ad spend

The Morrison government splurged almost $20 million in the four months leading up to the May federal election on promoting its road and rail plans.

However, spending on other phases of the Building our Future advertising campaign in 2016/17 and 2017/18 - the period well before the election - totalled only $336,000.

Labor infrastructure spokeswoman Catherine King said the pre-election spending - which also included $6 million spent in a single week - was all about gaining votes.

"While Australian communities are screaming out for transport upgrades, this agenda-less Morrison government is only interested in playing politics," she said.

An auditor-general report released on Monday called for a rethink of the decade-old rules around government advertising campaigns, which are independently assessed before money is authorised.

"A decade on, this area of government administration remains contested, with an ongoing focus on the discretion inherent in the framework and the long-term trend of increased campaign expenditure before elections," the report found.