The report, published last week, said that 39 per cent of staff reported developing physical or mental health issues as a direct result of working for the charity.
The review of the charity’s work environment was carried out by the KonTerra Group after the suicides of Amnesty staff members Gaetan Mootoo and Rosalind McGregor last year. Separate reviews of the two deaths also took place.
Unite said the report painted "a very bleak picture" of Amnesty International’s leadership team under the secretary general of the time, Salil Shetty, and called for a radical change to senior leadership at the charity.
In a statement, the Unite branch at Amnesty International gave its full support to Kumi Naidoo, who took over from Shetty in August 2018, and welcomed the initiatives he had already put in place and his emphasis on changing the culture of the organisation.
But the statement said the branch had no confidence in other members of the senior leadership team who were in post before the deaths of Mootoo and McGregor.
"It is unfeasible to imagine that, given the findings in these reports, the senior leadership team can be considered as part of the solution," the statement said.
"The union has always been committed to changing the working culture of Amnesty in a constructive and cooperative manner and looks forward to working on this with the new secretary general."
The statement said that none of the matters raised in the report should have come as a surprise to the charity’s senior management and human resources team because these were issues raised "numerous times over the years" by the union and staff.
Alan Scott, regional coordinating officer at Unite, said the report was a damning indictment of the toxic and dysfunctional working culture at Amnesty.
"It is absolutely intolerable that workers at Amnesty experience bullying, targeting and power misuse, and the previous leadership team must take full responsibility for these failures," he said.
"It is imperative that the findings of this report are not ignored and Amnesty now works closely with Unite to end the appalling working culture that currently exists."
The review of Mootoo’s death found that the charity had not breached its duty under English law to provide a safe system of work for the 65-year-old researcher. The review concerning Rosalind McGregor, a 28-year-old intern working in the charity’s Geneva office and previously at its offices in Mexico City, highlighted concerns about the charity’s monitoring of her workload but concluded there was no breach of the charity’s duty of care.
Amnesty International did not offer a specific response to Unite's comments, but in response to the working culture review, Naidoo said he wanted to repeat a promise he had made previously, that "where individuals have been found wanting – in SLT or elsewhere – this will be addressed".
This might include disciplinary action if necessary, he said.