Facebook whistleblowers Frances Haugen and Daniel Motaung came from very different parts of the social media platform’s ecosystem, but when they met for the first time in front of an audience in London Tuesday, they shared a message for anyone who has witnessed wrongdoing: Speak up.

Haugen, a former employee at Facebook’s Silicon Valley headquarters who leaked thousands of pages of internal documents last year, was joined onstage by Motaung, a whistleblower who was fired from his job as an outsourced Facebook content moderator in Kenya after leading a unionization effort. He currently lives in poverty in his home country of South Africa, and is pursuing a legal case against Facebook’s parent company Meta, and Sama, the outsourcing company that directly employed him.

“Daniel’s struggle is part of a long history of the struggle of labor,” Haugen told the audience who had assembled at King’s Place in London to hear the pair in conversation. The panel was organized by Foxglove, a legal NGO that is assisting Motaung with his case against Meta and Sama. Foxglove’s co-director Cori Crider was also on the panel, along with Mercy Mutemi, Motaung’s lawyer in Kenya. The event was funded by Reset, a progressive tech lobbying organization that works with Haugen.

“People fighting for each other is why we have the 40 hour work week,” Haugen said. “And we need to extend that solidarity to the new front, on things like content moderation factories. We can do this. We’ve done it before and we’ll do it again.”

It was the first time that Motaung, who suffers from severe post traumatic stress disorder (PTSD) as a result of his time as a content moderator, had addressed an in-person crowd since he blew the whistle in a TIME investigation earlier this year.

Read More: Inside Facebook’s African Sweatshop

Motaung said on stage that his legal case against Facebook and Sama was not just an attempt to achieve justice for himself and his colleagues, but also part of his healing journey. “For me, an easy way out is not an option,” he said. “It’s that drive to bring about change. It’s that drive to see justice. It’s that drive to make sure that I feel. It’s that drive to make sure that I become a human again, because I feel like a zombie most of the time.”

In one of the event’s most powerful moments, Haugen asked Motaung a series of rapid fire questions about the allegations in his lawsuit that he and his colleagues were hired under false pretenses. “If they had worded the job description and they had said, you will have to look at graphic violence every day, would you have taken the job?” Haugen asked.

“No,” Motaung replied.

“If they said you will have to watch people hurting innocent people, would you have taken the job?”

Again, Motaung’s answer was a one-word “No.”

“If they had said you will not be able to talk about how you feel after you do this, would you have taken the job?” Haugen asked, referring to the non-disclosure agreements Sama employees are required to sign.

“No,” Motaung said.

Haugen then told the crowd that she also suffers from PTSD due to medical trauma. She said that the non-disclosure agreements that Facebook content moderators are required to sign likely increase the risk of them developing that mental illness. “One of the most important things you need to prevent PTSD is to be able, while you’re undergoing trauma, to talk about what you are experiencing,” she said. “When people sign contracts where they can’t talk to their own family members about what they are going through, you’re substantially increasing the chances they’re going to have PTSD. It’s unethical and inhumane.”

Read more: Inside Frances Haugen’s Decision to Take on Facebook

The effect Motaung’s illness has had on his everyday life was demonstrated shortly after this exchange with Haugen when he unexpectedly left the stage for five minutes to take some time alone.

Motaung had previously told TIME that, due to the nondisclosure agreement he signed, he could not talk with his family about what he had seen on the job in Kenya, nor why he had lost so much weight.

“I just want to be honest with you guys: PTSD is real,” said Crider, the co-director of Foxglove.

After Motaung returned to the stage, an audience member asked if he would choose to blow the whistle again. His answer was clear. “Yes I would, definitely, without a doubt. I would do it again.” He urged others to speak up, too. “The most important thing you need to know is that there are organizations out there that can back you up,” he said. “You need to come out because if you don’t you will simply die in silence, and there is nothing good about that.”

“I speak for labor. I speak for workers,” he went on. “The exploitation is across the board, it’s not only Facebook.” He hinted that he hopes to help facilitate what he called a “global union” of outsourced workers. “Right now they are standing alone, and they feel alone. They are being taken for granted. Something has to happen. I’m sending a message to them: Unionize. Come together. Speak.”