A zoo in Japan has issued a stern warning after a visitor is seen aiming a laser pointer at Punch, the baby macaque who became a viral sensation, in an online video.

The Ichikawa City Zoo and Botanical Gardens in Chiba prefecture told The Japan Times on Thursday that it received a call a day earlier about a YouTube video posted last week showing someone shining a laser on Punch.

“It’s unacceptable,” Takashi Yasunaga, who is in charge of the city’s zoo division, told the newspaper.

Pointing lasers at any animal would cause them considerable stress and, if aimed at the eyes for too long, could result in blindness, Yasunaga said.

Punch and the rest of the monkeys in Monkey Mountain were not harmed but the zoo has stepped up its security around the enclosure by increasing patrols and widening the restricted viewing area.

“We will take firm action, such as immediately expelling laser pointer users from the zoo,” an official told Kyodo news agency, calling the act “extremely dangerous”. It has also warned against using camera flashes.