The operators of Iconsiam apologised on Tuesday after one of its guards was videoed assaulting a student protester who was expressing political opinions in the complex.
The Iconsiam Facebook page promised an investigation and punishment for the guard if he was found guilty of slapping the student.
The pro-democracy Ratsadon protest group named the victim as Benja Apan, a 21-year-old student from Thammasat University.
Benja is among protesters charged with lese majeste over a demonstration at the German Embassy on October 26.
Ratsadon added that she was restrained by the guard as she tried to leave the complex. Her friend attempted to livestream the fracas via social media, but another guard tried to snatch the smartphone from her hand. Benja was then slapped by the guard and the livestream ended, said the group.