Senior Labor frontbencher Penny Wong has clashed with high-level bureaucrats over government spending on advertising, accusing the coalition of a cover-up.

The clash came as former prime minister Malcolm Turnbull took a dig at government advertising at a book launch in Sydney on Tuesday.

"There is a lot of government advertising on at the moment and most of it is not particularly compelling," he said.

At a Senate estimates hearing in Canberra, Finance Department officials confirmed 15 campaigns worth more than $250,000 have been approved this financial year but refused to detail the extent of spending.

Senator Wong branded the response "outrageous" after demanding answers on how much was being spent in the lead-up to the federal election.

"They have refused to tell Australians how much of your money is being spent on these campaigns," she told the hearing.

She said AusTender data showed the government had ticked off $136 million for advertisements since the start of the year.

Ministers have argued this figure is misleading because it refers to the value of contracts approved rather than how much is being spent on ads in that period.

Assistant Finance Minister Zed Seselja said the government would not be providing rolling updates of advertising spending.

"This minister is not going to tell you how much of your money is being spent - brilliant," Senator Wong responded.

Senator Seselja said the coalition was providing more information than Labor did when it was last in government.

After being pressed by Senator Wong, finance bureaucrats said the total amount of spending approved were a confidential cabinet matter.

Department secretary Rosemary Huxtable said the latest reliable estimate was $46 million had been spent up until January during the current financial year.

Senator Wong repeatedly asked if spending was $1 million a day in the lead-up to the May poll, but the finance department doesn't produce daily totals.

"You've made up a number - it's completely fabricated," Senator Seselja said.