Unite claims that the charity sector shares with the health sector the highest level of workplace bullying in the UK economy.
"It is probably the most prevalent issue that we deal with in charities," said Rachael Maskell, not-for-profit officer at Unite. "I think the reason bullying is prevalent in the sector is that when it happens management are not trained to deal with it."
This week, the union is sending out Dignity at Work campaign packs to its representatives in the sector in a bid to persuade voluntary organisations to sign up to the campaign and pledge to deal with the issue.
The union is also carrying out research on bullying in the voluntary sector.