Clubs found guilty of salary cap rorting may face fines of up to $2 million as the NRL considers doubling the financial penalties that can be imposed for serious breaches.

NRL CEO Todd Greenberg revealed during a press conference on Wednesday about the investigation into alleged salary cap breaches by Cronulla that he had been asked by the ARL Commission to review the maximum fine clubs could receive.

While insisting the allegations against the Sharks were not "on the scale" of previous breaches and that all teams in the upcoming finals series were cap compliant, Greenberg said penalties had not matched an increase in funding for clubs.

The maximum fine has not increased since 2013 when the annual grant from the NRL was $7.1 million but clubs will each receive $12.5 million funding this season – more than $3 million above the $9.4 million salary cap.

"As the cap has gone up and grants to club have gone up, the imposition of fines hasn’t kept pace,” Greenberg said.

"That is something that the Commission has asked me to look at at the end of this year - do we need to have additional financial penalties over and above what we have historically had."

Parramatta were fined $1 million and docked 12 competition points in 2016, while Manly are appealing a $750,000 fine and $330,000 salary cap reduction for this season and in 2019 after being found guilty of cap breaches.

Greenberg said the allegations against Cronulla were not as significant as those breaches but as the investigation was ongoing he could not guarantee the Sharks 2016 premiership win would not be tarnished.

He also confirmed Cronulla coach Shane Flanagan would be interviewed by the NRL integrity unit, along with former chairman Damien Keogh and CEO Lyall Gorman, who is now at Manly.

"As we delve into the details there are a number of people we need to come forward and speak honestly, openly and truthfully about their experiences inside the club," Greenberg said. "That will include current and former staff and executives."

The Sharks self-reported concerns about a possible breach in 2015 when new CEO Barry Russell took over from Gorman in March this year.

Gorman, who was in the role from November 2014 until the end of the 2017 season, told NRL.com the first he has heard of the Sharks investigation was when news broke on Tuesday night.

Greenberg confirmed the issue reported by the Sharks, who have also had a change in chairman after Dino Mezzatesta took over from Keogh in June 2017, was related to an undisclosed third-party deal.

There are a number of people we need to come forward and speak honestly, openly and truthfully.

Todd Greenberg

Investigators are studying "tens of thousands" of documents seized by the NRL integrity unit and Greenberg said a "thorough analysis" would determine whether there had been further breaches in 2016 or 2017.

However, he said all 16 NRL clubs were salary cap compliant and revealed the Sharks had spent more than $500,000 below the $9.4 million ceiling for player payments.

"On the matters before me, as they currently sit, this is not on the scale of previous clubs under investigation like Manly, the Eels or further back like the Storm," Greenberg said.

"The work we're doing goes back historically a number of years. Just because a club has a salary cap breach potentially in a certain year doesn’t necessarily mean that we strip titles or you take competition points.

"A lot of times relatively modest salary cap breaches result in fines. I don’t know what the outcome of this will be but from what has been presented to me today it is nowhere near the scale of some of the other things I have seen come forward.

"… Importantly, on the information available to us, every club in the NRL, and that includes the Sharks, are cap compliant in 2018. The 2018 finals series will not be affected by this investigation."