Latrell Mitchell and Josh Addo-Carr have both been fined $50,000 for breaching self-isolation protocols.
Tyronne Roberts-Davis and Nathan Cleary have both been fined $10,000.
All four players have been also been given a one-match ban, which has been suspended for the remainder of the season, after the NRL announced they had brought the game into disrepute.
Sixty per cent of the fines have also been suspended for the remainder of the season.
The sanctions were handed out less than an hour before Mitchell and Addo-Carr were charged by NSW Police over firearm offences.
Mitchell, 22, has been issued with a Future Court Attendance Notice for the offence of give firearm to person not authorised by licence/permit.
The Rabbitohs star had his firearms licence suspended with a number of firearms seized by police.
Acting CEO Andrew Abdo explains player sanctions
Addo-Carr, 24, who was allegedly filmed using one of Mitchell's firearms on the weekend, has been issued with a Future Court Attendance Notice for the offence of use unauthorised firearm.
Mitchell and Addo-Carr are expected to appear at Taree Local Court on August 4.
The NRL announced the players had each shown a blatant disregard for public health orders, guidelines and advice and in doing so have brought significant reputational damage to the sport.
The penalties allege that each player has brought the game into disrepute and do not pass judgment on any ongoing police investigations.
Australian Rugby League Commission chairman Peter V’landys said "the players have a responsibility to the game and community".
"It is important that, in these challenging times, we all have to work together to combat COVID-19 and compliance with public health orders is a critical requirement,’" he said.
"The players have to understand that they are putting the game and the community at risk by their actions.
"It’s certainly hard to accept such behaviour when the game is doing everything it can to persuade the community that its players are responsible and behave appropriately.
"The penalties have been structured so as to give these players one further opportunity to demonstrate that they can be trusted. If they contravene again, then those parts of the penalty that have been suspended will be activated and they may also be subject to further sanction."
NRL acting CEO Andrew Abdo said the game acted quickly to send a clear message to all players and the wider community.
"It's not the circumstances I'd expect to do my first press conference. The actions of our players that have come to light over the past couple of days has been disappointing and we needed to act swiftly," he said.
"We're all under pressure, we all face restrictions, we're all away from our usual circumstances.
"This is on all of us and our players are no different, they are role models in our society. We have bold and ambitious plans to return to the field as soon as we practically can.
"It's important the players understand that they are held to a higher account. I think we've got to look at this in two phases. The players are not in the care of the clubs at the moment, they've been stood down and are subject to the public health order.
"As we enter into the training period and the second phase the protocols are significantly higher. We are all humans, humans make mistakes and there are consequences for those mistakes."
In explaining why Mitchell and Addo-Carr received harsher sanctions, Abdo said each matter needed "to be handled on individual merits".
"What's happened with Latrell and Josh is they've gone on a planned holiday in which there were activities that involved camping and a wide number of people," he said.
"That's very different to someone being at home and whilst it's still against the public health order, it's a very different context to someone attending to your home in a very short and unplanned period of time.
Latrell explains social distancing slip-up
"I'm not going to make a comment on everyone's perception around what's appropriate from a cultural perspective. The matters have been treated on the actions of the individual. This has nothing to do with culture or race.
"I have multiple concerns and as you can imagine I am focused on a number of things. We are working day and night to get the competition back up and running.
"Any setback is a setback for all of us as a game but I'm not concerned about these particular issues derailing any of those discussions.
"We take this matter very seriously. I know a lot of our players are doing the right thing and if they're not they'll face sanctions.
"The match ban gives them an opportunity to think about their actions going forward and give the playing group an idea of what's at stake here.
Why Addo-Carr reached out to Latrell
"There's a very detailed set of protocols that are with the clubs that are yet to be finalised. We'll talk about that when the time is right."
Abdo, in the statement issued by the governing body, said NRL players must set the standards for the public to follow.
"The sanctions proposed today are stronger than fines which can be imposed by authorities because we hold our players to a higher standard and they must set a higher standard for the community,’" he said.
"We are focused on resuming the competition on May 28, something our fans and stakeholders are excited about. Players who do not comply with community and NRL protocols will face sanction."
All four players will have five days to respond to the breach notices before a final determination is made.
"We've done what we think is fair in the actions. Upon reflection I think this will affect the players," Abdo said in his media conference.
"We've reached out to all the players, they have the opportunity to respond, they have five days and we will engage with them and take it from there.
"It's an absolute privilege to be servicing the game. I don't think I could have come up with a scenario we're in with a global pandemic. I'm going to work tirelessly in the day and night to do what we can."