A female teacher punished 36 students aged 7-8 years old by piercing their lips with the same safety pin after none of them had admitted to spitting out chewing gum on their classroom's floor.

The incident happened on Thursday morning at Wat Dan Samrong School in Samut Prakan when a 27-year-old teacher stepped on the gum. The teacher asked the students who spat the gum out, but no one owned up.

She asked another female teacher, 50, for help. The older teacher used the sharp point of a safety pin to pierce into the inner lip of each student in the class.

One of the students' parents on Friday filed a complaint with local police against the two teachers. Other parents also demanded the school take responsibility and expressed concern that the pin could have infected their children.

The school director suspended both teachers from their jobs after they admitted to their actions.

The 50-year-old teacher apologised and said she wanted to teach the students to be responsible. She said the safety pin was new.

Police will press charges against the two teachers after questioning all students.