Cronulla coach Flanagan was provisionally deregistered by the NRL on Wednesday for breaking strict rules by communicating with the club while suspended in 2014.

Cronulla have also been fined $800,000, with both the club and Flanagan having until the end of January to appeal their punishment.

Flanagan is unable to have any official involvement with the club in that period.

The NRL found five pages of emails between Flanagan and the Sharks regarding recruitment after current CEO Barry Russell self-reported a potential salary cap breach in 2015.

No other Cronulla officials have been punished because most are no longer in the NRL, including then-CEO Steve Noyce and then-football manager Darren Mooney.

"We understand the impact this will have on Mr Flanagan and on the Sharks as they prepare for the 2019 season," Greenberg said.

"But we cannot stand by and allow the game's rules to be broken."

Flanagan had been stood down by the game in 2013 for 12 months - three of which were suspended - over the administration of illegal supplements in 2011.

The club was also fined $1 million - $400,000 of which was also suspended.

As part of the penalties, Flanagan was banned from corresponding with the club, an edict he is alleged to have broken just weeks into his suspension.

Flanagan's ban began in December 2013 but the NRL says emails prove he was involved in discussions over medical procedures, coaching structures and player talks.

In April 2014, the Sharks re-signed Flanagan for an extra three years and his manager requested the NRL relax his suspension. The governing body declined.

But Flanagan continued to involve himself in discussions over the club's future, including the possible recruitment of utility Blake Austin.

The NRL said the integrity unit continued to meet with both Sharks representatives and Flanagan's manager to ensure the coach had no contact with the club.

Both parties had repeatedly denied any ongoing communication.

Towards the end of his ban, Flanagan wrote to the NRL unequivocally stating that he had no involvement in potentially signing players during his suspension.

Asked to describe Flanagan's conduct, NRL boss Todd Greenberg said: "Disgraceful.

"Fundamental to the rules of the game and the integrity of the game that we work in is people being honest and truthful

"It cuts to the very core of the fabric of what the game's rules stand for and we can't sit around and watch that happen under the way the rules are governed."

When he returned from his ban Flanagan went on to be hailed as one of the best coaches in the game after leading the Sharks to their first premiership in 2016.

Yet when Russell self-reported salary cap irregularities midway through this year, investigators unearthed the email correspondence.

"We've had access to the servers at the club so we've trawled through a number of emails. The evidence in front of me to make this decision was very strong," Greenberg said.

He met with Sharks chairman Dino Mezzatesta and Russell to inform them of the NRL's decision early Wednesday.

Flanagan was invited to the meeting but declined to attend.

Australian Associated Press