Cincinnati beat New York at Red Bull Arena in a penalty shootout on Saturday, advancing to the semi-finals of the MLS Playoffs.
"After the Nov 4th NYRB/FC Cincinnati match, a player gained unauthorized entry into the Officials' locker room & was forcibly removed by stadium security while acting in an aggressive & hostile manner," the Professional Soccer Referees Association (PSRA) said on social media.
"No one's safety should ever be at risk & we expect MLS to act accordingly."
PSRA referees officiate matches for MLS, the National Women's Soccer League (NWSL) and the United Soccer Leagues (USL).
The PSRA did not confirm which player was removed or the nature of their dispute.
"Major League Soccer is aware of the report of a player gaining unauthorized access into the officials’ locker room," the league said in a statement.
"The safety of PRO officials must never be compromised and an investigation into this matter is being conducted."
