Just a short stroll from Labor's Sussex Street headquarters is a Chinese restaurant called The Eight.

Key points: Donors pledged $100,000 to the Labor Party at a fundraiser before the March 2015 state election

Donors pledged $100,000 to the Labor Party at a fundraiser before the March 2015 state election The donations came in the form of 20 donations of $5,000 — the maximum amount allowed from an individual

The donations came in the form of 20 donations of $5,000 — the maximum amount allowed from an individual ICAC is investigating whether the donations were genuine

Located on level three of a busy shopping centre, it is not especially eye-catching.

However, a Labor fundraising dinner held there on 12 March, 2015 caught the attention of investigators from the Independent Commission Against Corruption (ICAC).

Just over $100,000 was pledged to the party that night.

Now, more than four years later, ICAC is beginning six weeks of public hearings to investigate whether Labor was receiving cash from illegal sources.

And if it was, investigators want to know who knew about it.

They are calling their inquiry Operation Aero.

A number of leading ALP politicians were present at the 2015 dinner. ( Facebook )

The fundraising feast was well-attended.

Then-Labor leaders Bill Shorten (federal) and Luke Foley (state) were there, along with federal shadow treasurer Chris Bowen and Kogarah candidate, now state frontbencher, Chris Minns.

There is no suggestion of wrongdoing on their part.

Just weeks from the NSW election, party officials hoped the Chinese Friends of Labor fundraiser would help boost their campaign war-chest.

In the run-up to the March 2015 NSW election, political donations to NSW political parties were capped at $5,000 per year.

So even if an individual wanted to donate a much larger amount — say, $100,000 — they were banned from doing so.

The $100,000 donated on or around the night of the dinner came in the form of 20 donations of $5,000.

On the face of it, the donations were perfectly legal. They were declared.

But the neat bundles of $5,000 have attracted suspicion.

The 'straw-donor' theory

ICAC is investigating whether those donations were genuine, or whether they were made by "straw donors".

A "straw donor" is someone who puts their name to a donation that they did not truly make — which is against the law in NSW.

Huang Xiangmo (second from left) with Ernest Wong, former prime minster Julia Gillard and Sam Dastyari. ( Supplied )

Prior to these public hearings, ICAC investigators have been speaking to donors, party officials and others involved in the party's fundraising efforts.

One of the people they have been asking questions about is Chinese billionaire property developer Huang Xiangmo, who also attended the dinner.

Mr Huang has donated generously to both major parties since he came to Australia in 2011.

He paid a personal bill for former Labor senator Sam Dastyari, who held a media conference with the billionaire to voice support for Beijing's stance on the South China Sea dispute.

Mr Dastyari resigned following reports that he had visited Mr Huang's home and warned him that Australian spies may be watching him.

However, Mr Dastyari said he was visiting Mr Huang to end their relationship "face to face" and insisted he had always acted with integrity.

Mr Huang has since had his Australian permanent residency cancelled and is stranded overseas.

NSW Labor has "quarantined" the $100,000 until the investigation is complete.