She was speaking at the Truth and Reconciliation Commission's hearings on the media under apartheid, at the SABC's head office in Johannesburg. Mayet said black journalists formed the union in 1973 when they felt a need to express themselves.
She said she was unable to remember if one of the other reasons why it was formed was because it was illegal for black people to join whites in unions.
She was also unable to say if one of the other reasons was because black journalists felt they were unable to represent and express themselves under the white-dominated South African Society of Journalists.
She said she and her colleagues received support from many outsiders when police started arresting the union's members.
The union started taking off in a significant way in 1975 when it started holding regular meetings and brought out a newspaper, The Voice.
Their publication and the union was banned in 1977 in the aftermath of the Soweto Riots, but a new organisation, with the same aims, was immediately formed, calling itself the Writers' Association of South Africa.
Members of the union included an array of present-day media personalities like Joe Tloloe, Zwelakhe Sisulu and Phil Mtimkulu. Their main aim was to tell the truth and, being black, this immediately attracted repressive action from the state.
After the UBJ's 1977 banning, police action became more concerted and more members were arrested in 1978 as the union continued trying to live up to its motto: to tell the truth.
Mayet and Mtimkulu were arrested on a trumped up charge of theft after they had removed the union's funds from its bank account in 1977, but this had been a precautionary action because they feared foul play at the height of state repression in that year. They were both acquitted in 1978.
"I personally was not a political person, but the problem was, if you were black in those days, you were political whether you liked it or not," Mayet said.
She asked the commission to investigate what happened to the union's assets which were confiscated in 1977.
Mayet expressed regret that none of the union's former members had helped her in compiling a report for the commission, despite her attempts to contact them.