The gathering, at house of Dragons' player Paul Vaughan, breached both NSW government public health orders and the NRL's level four biosecurity protocols.

The NRL Integrity Unit is in the process of investigating the incident, with punishments expected to be handed down on Tuesday.

De Belin initially escaped punishment, the police fining 12 players and Vaughan's wife on Sunday.

He was, however, added to the list on Monday, NSW Police confirming a 30-year-old man has been slapped with a $1000 fine.

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"A 14^th person has been issued with a $1000 fine after further investigations into a gathering at a home in Shellharbour at the weekend," NSW Police said in a statement.

"Officers from Lake Illawarra Police District attended the home about 9.40pm Saturday, responding to reports of visitors at the location.

"One woman and 12 men, aged between 21 and 30, were issued with Penalty infringement Notices (PINs) for breaching stay at home directions.

"Following inquiries, another 30-year-old man was identified today, as being at the home; he has now been issued with a $1000 PIN for breaching a stay at home direction."

De Belin joins a host of Dragons big names in receiving fines, the group gathering at Vaughan's house after Friday night's golden-point win over the Warriors.

The former NSW forward has only recently returned to the playing field after spending 2.5 years out of the game while he fought sexual assault charges. The charges were eventually dropped after two hung juries.

It is understood the other players involved are Corey Norman, Zac Lomax, Josh McGuire, Jack Bird, Kaide Ellis, Blake Lawrie, Matt Dufty, Daniel Alvaro, Tyrell Fuimaono, Gerard Beale and Josh Kerr.

NSW Premier Gladys Berejiklian expressed her disappointment when asked about the incident during her daily press conference, the politician urging residents to stay at home.

"It is disappointing when anybody does the wrong thing, it doesn't matter what your profession is," Berejiklian said. "It is just disappointing because every time somebody knowingly does the wrong thing it jeopardises the rest of us."

NSW Health Minister Brad Hazzard was also frustrated people continue to flout health orders despite the risk of fines and the potential extension of Greater Sydney's lockdown should coronavirus cases rise.

"When you hear of parties going on in the middle of a lockdown you have got to say where is - what is the thinking of some of these people?" Hazzard said.

"As the Deputy Commissioner said, I am heartened by the fact that by far the majority of people are doing exactly what we would want them to be doing.

"I would say that those people who are thinking that the rules are somehow not for them, that they are more entitled than the rest of us not to listen, you actually have to listen because you may be the people who spread this and keep us in lockdown for a lot longer than the rest of the community would like."