The commission sent the casino a notice of noncompliance with the state's pandemic standards and the guest who held the party faces a $500 penalty, commission members said.
“This is much more serious than a guest being disturbed by noise, and certainly whatever measures they had before were not effective enough,” commissioner Gayle Cameron said during a remote meeting.
The state has a 25-person limit on indoor gatherings, the Associated Press reports.
The party was an “egregious" violation, commission Chairwoman Cathy Judd-Stein said.
“The stakes are too high for anything but full compliance with those safety standards,” she said.
The casino has instituted new rules that include limits of four guests per room or eight guests in a two-bedroom suite.
Additionally, the casino has boosted security and is more aggressively monitoring the amount of food and drink being brought to rooms in an effort to make staff better able to recognize the size of large gatherings, according to the gaming commission.
Several reservations have since been canceled, evidence that the stricter rules are being noticed by guests, said Bruce Band, the commission's assistant director of investigations and enforcement.
“Encore seems to be holding fast to their new rules and really sticking to their guns about what they’re trying to get their guests to abide by them,” Band said.
The state's three casinos were closed for about four months because of the pandemic but were allowed to reopen in July at limited capacity.