Anti-corruption watchdog Transparency International has been accused of promoting a “toxic” internal environment of bullying and harassment, making it the latest high-profile charity to come under fire over its workplace culture.

Seven current and former staff members said the organisation had “failed in its duty of care” to staff. They accused managing director Patricia Moreira of promoting a culture that enabled “bullying”, silenced critical voices, and used “gagging orders” – confidentiality clauses in termination agreements. Leaked internal emails and documents including a staff survey corroborate their accounts.

Transparency International – which operates in more than 100 countries – is known for championing whistleblowers’ rights and increased transparency from governments and corporations. But whistleblowers said the internal working culture at TI’s headquarters in Berlin was increasingly reminiscent of opaque and authoritarian organisations that the body seeks to hold to account.

“I was working myself into sickness,” said one former employee who resigned recently. “I’m a small person anyway, I’m 52 kilos. But because of stress I was down to 44.”

The allegations are the latest in a series of implosions in the aid sector. In May 2018, Gaëtan Mootoo, an Amnesty International researcher based in Paris, killed himself, sparking an outcry over claims about the human rights charity’s neglect of its workers. Oxfam, the Sunlight Foundation and Save the Children have been mired in allegations of sexual misconduct.

Each of the whistleblowers echoed fears that TI’s environment was dangerous for its staff. One staffer said the loss of colleagues in their department meant sometimes sleeping at the office to meet deadlines. “What we saw at Amnesty is what we see at TI. It’s just that nobody has committed suicide,” the interviewee said.

Moreira told the Guardian the organisation prioritised the wellbeing of staff. “TI is what its people are.” Referring to two employees who left the organisation, who said working there had affected their mental health, Moreira said: “I feel extremely sorry in those cases.”

Interviewees said managers “targeted” staff and “bullied” them into resignation – sometimes by assigning them unrealistic deadlines, imposing travel bans that prevented them from completing their duties or singling them out.

TI underwent a series of management experiments from 2016 onwards due to a shortfall in expected funding. The organisation’s management hierarchy was replaced by “holacracy”, a system that is supposed to distribute power and boost self-governance. After a rapid succession of short-term directors and staff culls, Moreira was appointed managing director of TI in October 2017. She decided to abandon the holacracy system and reintroduce managers.

Moreira unilaterally appointed senior managers, whistleblowers said, contravening TI’s internal standards for good governance. Some staff were told not to apply for promotions, that they would “never be eligible”. Moreira denied doing this, saying staff were always welcome to apply for any positions, but said she may have made errors in communicating that.

In August 2018, TI’s works council – a body that represents TI’s employees – organised a staff survey, which recorded answers from 92 employees. The survey showed that 66% of respondents had observed or experienced bullying, and that one in five people thought sexual harassment was an issue at TI.

Moreira felt the survey, conducted 10 months after she was appointed, was premature. In an email sent to staff before the results were posted she said that the survey was “not appropriate and not relevant”.

Moreira called a staff meeting after the results were posted and told staff not to record minutes. She said that staff needed more time to get used to her management style and that she would not “engage with” the survey, interviewees said. Minutes from a board meeting suggest that TI’s board discussed the survey’s results and noted that the allegations of bullying, if true, were a cause for concern.

Whistleblowers said they asked for workshops on how to deal with bullying, but management did not conduct any, or address the concerns about systemic bullying at the organisation. “We were saying we have credible concerns,” a whistleblower said, “that we have a toxic work environment, that we worry about the mental health of our colleagues. Our employer was unwilling to engage.”

At a meeting about sexual harassment, Moreira was heard saying that the survey’s results on sexual harassment were incorrect and that staff did not understand what sexual harassment was. “I knew of at least three different cases of sexual harassment,” one whistleblower said. “[One employee] was aware of the same case I knew of. He stood up and contradicted [Moreira]. That got him into trouble.”

The employee, who spoke up about staff concerns repeatedly, was singled out by managers, given unreasonable deadlines to complete projects and restricted from travelling to an important event. Eventually, the employee resigned.

“I lived through something. I went home and I couldn’t sleep,” the employee said. “It weighed on me. It weighed on my family. I just want validation of that experience.”

In a statement to the Guardian, Moreira explained that she was referencing an independent expert who had carried out a review of TI’s internal ethics infrastructure and who concluded that staff may have confused other workplace issues with sexual harassment.

“Authoritarianism has crept into Transparency International,” one whistleblower said. “Staff used to ask questions at meetings. Now even that is censured or looked on as disloyal.”

Whistleblowers also spoke about how reporting mechanisms for sexual harassment were eroded under Moreira. Previously, one whistleblower explained, there was a group of elected staff who would report complaints to the director. Moreira scrapped their roles and appointed one staffer instead, who according to whistleblowers would be obliged to divulge the complainant’s name to her.

Moreira said the new appointment was a professional with training on how to deal with staff complaints and was empowered to conduct independent investigations into complaints and escalate matters about senior management to the board. She said the role came with a duty of confidentiality to complainants. However she admitted that getting staff to trust the new ethics framework had been a “challenge” and that “the full deployment of the integrity system has not yet happened”.

In a phonecall with the Guardian, Moreira emphasised that TI was going through “a challenging period of change”.

She said that though staff had left the organisation, she was committed to working with those who had stayed. “We have the important responsibility of creating a safe space and the right conditions for our staff.”