The two from DATACTIVE — Stefania Milan and Becky Kazansky — had agreed to act of co-ordinators of the Digital Society and Surveillance theme at the conference, and had accepted a panel proposal from the Data Justice Lab at Cardiff University.

The four participants from the Cardiff organisation were to be Lina Dencik, Arne Hintz, Joanna Redden and Fieke Jansen.

The APC has Palantir down as a platinum sponsor for the event, along with Microsoft, Vodafone and Zggo.

In a statement on Wednesday, the six said: "Our decision to withdraw stems from an active refusal to legitimise companies accused of enabling human rights abuses, and a concern with the lack of transparency surrounding sponsorship."

They pointed out that Palantir developed technologies for the military, law enforcement and border control.

"The deployment of Palantir’s technologies has raised widespread concern among civil liberties and human rights advocates," they said.

"Reporting shows that, in the United States, Palantir has played an important role in enabling the efforts of the ICE (Immigration and Customs Enforcement) to identify, detain, and deport undocumented immigrants, refugees, and asylum seekers."

In June, workers at retail giant Amazon asked their owner, Jeff Bezos. to cancel the contract for hosting data-mining company Palantir on its cloud, with a threat that else, they would not build the platform that powers ICE.

The six researchers said that ICE had carried out indefinite detention of thousands of children who have been separated from their parents. "This indefensible policy has come under strong criticism from the United Nations and prompted an alliance of technology workers and affected communities, to call — so far, unsuccessfully — for Palantir to cancel its contracts with ICE," they said.

They said the organisers of APC had not been open about the sponsors, with sponsorship agreements not being revealed until the last minute.

"Though we acknowledge the complexity of corporate sponsorship, we note that other prominent tech policy conferences, such as the Computers, Privacy and Data Protection conference, have recently stopped accepting sponsorship from Palantir," the six said. "We thus believe this is a good moment for a larger discussion about how conferences should be organised in the future."