The Health Department and its portfolio agencies spent $433,000 of taxpayers' money on cabs in less than three months last year and the Department of Social Services put $221,000 on the meter in just four months.

Veterans' Affairs reported a $54,000-a-month taxi bill between July and October, spending a total of $216,000 for the period.

Six departments and number of smaller agencies have reported racking up taxi bills of $1.8 million in the first three months of the Abbott government, or nearly $30,000 each working day.

The overall taxi expenditure for the public service will be much higher, with the three largest departments - Defence, Tax and Human Services - yet to disclose the cost of their cab rides to the Senate committee that asked for the information in November.

The office of Public Service Minister Eric Abetz, whose party pledged before September's election to "stop the waste" and slash public service spending, referred questions on the spending to the Finance Department.

A spokeswoman for Finance Minister Matthias Cormann said the department did not know what the whole-of-government taxi bill might be, but that the government expected all cab rides to be for official business.

"The government expects that all departments and agencies adhere to their chief executive instructions or other relevant operating guidelines to ensure the appropriate use of taxis," the spokeswoman said.

The Department of Health said the money spent on taxis by its "core department" and 21 portfolio agencies was necessary to support its work.

''[The department] undertakes travel to meet with key stakeholders to ensure health programs are adequately supported," it responded in a statement addressing a question on notice from Labor senator Joe Ludwig.

"The department funds the travel of members of expert committees which advise on a range of professional, consumer and community issues with the aim of better targeting health programs and health expenditure.

"Health reform initiatives require consultative and public communication activities."

A spokeswoman for the Department of Social Services said the department had a national network of offices and needed "to engage with our clients and service providers around Australia".

"Expenditure on taxis is necessary," the spokeswoman said.

"A significant proportion of these costs are associated with staff working in the important area of indigenous affairs, whose work often involves travel to and from regional and remote areas of Australia.

"Another large portion of these costs was incurred by staff working in independent portfolio agencies such as the Social Security Appeals Tribunal, and by staff working in support of the National Disability Insurance Agency."

Veterans Affairs justified its $54,000-a-month cab bill in its answer to the senator, saying that taxis were used only for official business.

"Taxis are used by DVA staff in conjunction with official travel … to travel from the airport to the DVA office; to travel to external meetings; and to accompany veterans attending commemorative activities," the department's answer read.

"Taxis are also used by veterans to attend DVA-related activities."