The allegations centre on two turbulent years
Both 2013 and 2014 were turbulent years for An Garda Síochána, culminating in the retirement of former Garda Commissioner Martin Callinan over the phone tapping controversy.
He would be replaced by his deputy commissioner Nóirín O'Sullivan.
But it was during this period that senior gardaí are alleged to have orchestrated a smear campaign against garda sergeant Maurice McCabe.
Those allegations were last year put in writing under the Protected Disclosure laws and formally submitted to the Tánaiste and Justice Minister Frances Fitzgerald.
The authors of the disclosures were Sgt McCabe himself, as well as Superintendent Dave Taylor.
As head of the garda press office, Supt Taylor was based in the Phoenix Park headquarters when the alleged smear campaign was unfolding.
After Martin Callinan had departed from the force, Supt Taylor was put under formal investigation and later suspended for alleged leaks to the media.
The allegations have never been proven.
But last year, following a series of meetings with Sgt McCabe and his legal team, Supt Taylor decided to make the protected disclosure.
He is understood to have claimed that he was directed by former Commissioner Callinan to take a leading role in the alleged smear campaign.
And he is also believed to have claimed in the disclosure that other members of management, including Commissioner O'Sullivan, were complicit.
These disclosures led to a political storm after appearing in the media.
Under political pressure, Ms Fitzgerald appointed retired high court judge Iarfhlaith O'Neill to conduct a scoping exercise.
The report was completed in December and it was then sent to the Attorney General Máire Whelan for examination
Today, a commission of investigation will be launched led by Supreme Court judge Peter Charleton.