The union representing Canadian prison guards is calling for a public inquiry into the suicide of a female inmate in a women's prison in Ontario, arguing its members were prevented from doing their jobs in the case "every step of the way."

The appeal came as the Union of Canadian Correctional Officers released its own report on Thursday into the case of Ashley Smith, a 19-year-old inmate who was found dead last year at the Grand Valley Institution for women in Kitchener, Ont.

Three former guards and a supervisor were charged with criminal negligence in her death. Their preliminary hearing was to start on Thursday.

During a press conference, union president Pierre Mallette said local and senior Correctional Service Canada managers "were more concerned about public relations than what was happening inside our institutions for women."

Smith, originally from Moncton, spent years in the youth correctional system and had an established history of violence and self-harm.

The union claims guards were told not to intervene whenever Smith appeared to be harming herself, unless she stopped breathing.

The union further claims management made sure guards would refrain from entering Smith's cell during her almost-daily incidents of self-choking.

Smith had been serving a six-year, one-month sentence for offences committed as a young offender, including assault with a weapon and assaulting a peace officer, and would have been eligible for release in November.

In June, New Brunswick's ombudsman called for significant changes to how the justice system handles young people with mental health problems after his investigation into Smith's death.

Bernard Richard said the case highlights the need to change practices, particularly to divert youth with mental illnesses and behavioural problems away from the justice system by boosting services and foster care.

With files from the Canadian Press