A south Wales anarchist seeking damages for police infiltration of his group has criticised a decision to hold hearings into the complaints in secret.
The Cardiff Anarchist Network claim an undercover officer spent nearly five years in their group, forming sexual relationships with two members.
But complaints about the operation will be heard behind closed doors in an Investigatory Powers Tribunal.
Campaign group member Tom Fowler said it raised questions about open justice.
The case is being brought by 10 women and Mr Fowler, from Newport, involving both South Wales Police and the Metropolitan Police in London.
Some of the complaints involve the case of PC Mark Kennedy who infiltrated environmental groups.
His involvement with one group led to the collapse of a trial of protesters who had been accused of plotting to shut down a coal-fired power station.
It led to a review of how undercover officers are deployed and managed in 2012.
Some of the campaigners caught up in the Kennedy operation and the south Wales case are seeking compensation for the emotional trauma they suffered.
They also claim the Human Rights Act was infringed.
'Nature of democracy'
But the Appeal Court ruled on Tuesday that the human rights aspect of the case against the police must be heard in secret, at a special Investigatory Powers Tribunal.
The tribunals were set up in 2000 to examine complaints about potentially intrusive powers used by intelligence agencies in the UK.
Master of the Rolls Lord Dyson, Lord Justice Maurice Kay and Lady Justice Sharp said the tribunal did have jurisdiction to hear the human rights claims.
But Mr Fowler told BBC Radio Wales that it raised serious questions for him.
"I think the existence of the Investigative Powers Tribunal in the case should make any fair thinking person quite concerned about the nature of democracy and justice in this country," he told the Good Morning Wales programme.
"We are not talking about terrorism here. We are talking about some very basic democratic protests."
Mr Fowler claims their anarchist group was infiltrated by a police officer posing as a Northampton truck driver.
He said the individual went on to form sexual relationships with two women in the network group, cementing the group's trust with the police officer.
"We weren't necessarily looking for police officers in the ranks. He was quite natural. There were other people just like him who I knew, and still know, who are real people," said the campaigner.
"A key part of his infiltration technique was to be chasing after women.
"By being in relationships with these women they gained a level of trust within the wider group, because of those people being trusted."
Mr Fowler said the infiltration technique used against the group, in particular forming close relationships with its members, was not justifiable.
The claims for compensation by those bringing the complaints is now set to be heard in open court in January, while the human rights issues will be heard by the tribunal in private.