The SA Democratic Teachers Union (Sadtu) in KwaZulu-Natal says threats and the presence of firearms were commonplace at Masuku Primary School in Folweni - where a teacher was recently shot dead - over the past year.
Provincial secretary Noma Caluza told News24 on Wednesday that consistent discontent may have led to the killing of 48-year-old Sboniso Nyawose on Tuesday.
She said that he had been a strong contender for the permanent principal position.
A man is alleged to have entered the school premises and fired multiple shots at Nyawose while he was walking down a passage. He was hit in the head and abdomen.
She said the union was angry about the incident because they informed the department that a senior staffer who was recently hired, had often attended the school armed.
Caluza said that the staffer often carried his firearm to school in an attempt to intimidate teachers.
"Our members on the ground have said that he told teachers that if they continued to raise concerns with how the school was run, they would be shot."
This staffer carried a gun to his interview too, Caluza said.
Caluza said the local Sadtu chairperson in the Vela Makhanya branch had to get a protection order after receiving consistent threats from the member.
On Wednesday, GroundUp reported that another teacher, who asked not to be named, also said a senior staff member had been suspended from the school in January after "he started being aggressive toward everyone, including teachers".
The teacher said the senior staff member had been coming onto the school premises with a gun and threatened teachers and the school governing body (SGB) before he was suspended.
Department of Education spokesperson Kwazi Mtethwa confirmed that Sadtu presented the allegations to the provincial head of department.
"A full-scale investigation will be undertaken by the department."
Police spokesperson Colonel Thembeka Mbele said police were still in the "very early stages of investigation".
"The motive of the killing is unknown and is subject to investigation."