Communications Minister Mitch Fifield has faced hostile questioning about why he did not know the specifics of Ahmed Fahour's multi-million-dollar salary as chief executive of Australia Post.

Mr Fahour's $5.6 million pay deal for last financial year was seen as a factor in his decision to quit as chief executive late last week after his salary was publicly criticised by Prime Minister Malcolm Turnbull.

Senator Fifield was grilled by a Senate estimates committee, with questions mainly coming from Labor Senator Anne Urquhart, who appeared infuriated that the Government's shareholder minister was in the dark about Mr Fahour's exact pay deal.

"You say he was well remunerated. I would say someone on $100,000 was well remunerated. But you didn't have any idea as to what the amount was," a bemused Senator Urquhart said.

"I knew that the chief executive of Australia Post had a package that was several million dollars," Senator Fifield responded.

"I just think Minister that it's outrageous that someone who is a shareholder minister had no idea of the quantum of the executive of Australia Post," Senator Urquhart continued.

"Completely outrageous. It's just unfathomable."

Senator Fifield told the committee that he did not have a role in setting salaries and that Mr Fahour's package was determined by the Australia Post board.

"Yes, I was aware that the CEO Ahmed Fahour was well remunerated. Yes, I knew that his remuneration was in the millions of dollars, but did I go through his contract and break down the individual elements of his remuneration? No I didn't," Senator Fifield said.

The extensive questioning of Senator Fifield was the feature of the morning hearing, with Ahmed Fahour's appearance delayed until this afternoon.

The controversy over Mr Fahour's $5.6 million salary emerged a few weeks ago when the committee revealed the full details in the face of reluctance from Australia Post.

In the wake of Mr Fahour's resignation last Thursday, the Government announced that his replacement's salary would be determined by the government's Remuneration Tribunal rather than the Australia Post board.