Are consultants making so much money from the Federal Government that they're now treating departments as cash cows and openly dubbing it "The Dairy"?

Key points:

Federal Labor says consultants use the nickname because they "milk [the Commonwealth] for all it's worth"

Federal Labor says consultants use the nickname because they "milk [the Commonwealth] for all it's worth" Four companies have secured more than $1.7 billion in work in recent years

Four companies have secured more than $1.7 billion in work in recent years Consultancy firms defend their work but support calls for more transparency

That's the charge from federal Labor, which confronted the big four consultancy firms — Deloitte, KPMG, PriceWaterhouseCoopers and Ernst and Young — at a parliamentary inquiry on Friday.

The firms, which have won more than $1.7 billion in Federal Government business in recent years, say they are not aware of the nickname reportedly used by some Canberra-based staff who work with the Government.

The companies insist they are providing vital services and expertise, but former Border Force Commissioner Roman Quaedvlieg has described them as "a pack of predatory sharks hitting a bait ball in a feeding frenzy".

The Joint Committee of Public Accounts and Audit was prompted by concerns the firms were being unnecessarily hired at the expense of smaller players and value for money.

The committee's deputy chair, Labor MP Julian Hill, asked senior executives if they were aware of the nickname.

"It's a term that I was told by a couple of people is unkindly used for the Commonwealth, because you milk it for all it's worth," he said.

Senior executives defended the work of the consultants, saying they provide skills the public service does not have.

Finance Minister Mathias Cormann also defended the use of consultants, saying they had helped reduce the overall cost of government and keep departments flexible.

All executives agreed that there was a need for more transparency and pushed back against growing calls in the United Kingdom to split up their operations, amid concerns they have become an oligarchy.

Mr Hill also asked whether chief executives met socially to discuss government work, raising concerns about the potential for collusion to ensure market dominance.

That concern is based on Italy's anti-trust authority fining the big four $26 million for allegedly conspiring to divvy up public contracts, although executives insist that is not happening in Australia.