According to the section 2.23 of the statement of ministerial standards, "ministers' close relatives and partners are not to be appointed to positions in their ministerial or electorate offices, and must not be employed in the offices of other members of the executive government without the prime minister's express approval".
Under-fire Barnaby Joyce is set to be acting prime minister next week as one of his Nationals MPs says he has "100 per cent support" in the party.
On Monday a spokesman for Turnbull said Joyce had not breached the code because Campion was not the deputy prime minister's partner at the time of the staff appointments.
O'Sullivan said the Nationals base had expressed disappointment and frustration at Joyce's behaviour.
Questions are now being asked about Ms Campion's employment during her time with the federal Nationals, after the media advisor a year ago moved from Mr Joyce's office to the office of minister Matt Canavan and later to the office of Nationals whip Damian Drum.
"I would like to say to (my wife) Natalie how deeply sorry I am for all the hurt this has caused. And he's answered that", the prime minister said.
Mr Cassidy said "there might be something" but refused to comment saying it could not be substantiated.
She learned soon after that Ms Campion was two months pregnant with a child belonging to her husband of 24 years.
Mr Joyce received some sympathy from former prime minister Kevin Rudd.
The Canberra insider, whose husband works for the Prime Minister, told the "sun is setting" on the Nationals leader's career.
"The story, it's not a case that I didn't recollect it, it did not happen", he told reporters.
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'I would not expect to see Barnaby leading the Nationals into the next election.
'I just think the sun is setting on his career, and I can't see how he can survive'.
'He could have got out of it a bit better I thought if he had gone on and said, 'I really regret the pain that I have inflicted on my family, on my wife Natalie, and on my four daughters, I still really love my daughters'.
He noted Mr Joyce had said that freedom of information requests had not uncovered any breaches.
The marriage breakdown and the revelation of the affair are worrying some Nationals.
Deputy Labor leader Tanya Plibersek has called on the coalition to be transparent about Ms Campion's job trajectory after the relationship with Mr Joyce became known within government circles previous year.
Mr Joyce is pictured with his former wife of 24-years, Natalie.
Mr Joyce moved out of his Tamworth family home in December and later moved into the townhouse he now shares with Ms Campion.
He said the government needed to clarify the situation.
"I had no knowledge of the relationship between Mr Joyce and Ms Campion at the time", said Senator Canavan - who was Mr Joyce's chief of staff before entering parliament.
The publication reported Mrs Joyce was aware of the affair when she arrived as Mr Joyce's date to the Midwinter Ball in June.