Activists and the media are challenging a British judge's decision to allow the trial of two men accused of terrorism to be held in complete secrecy.
Two men, identified only as AB and CD, are due to stand trial behind closed doors, with the public barred from proceedings and journalists prevented from reporting the case when it begins this month.
Prosecutors successfully claimed that the highly unusual conditions were necessary for reasons of "national security".
The Times are among the newspapers fighting the secrecy order, stating it threatened "the centuries-old principle of open justice".
This contagion of secret justice has been spreading ... since before 9/11.
All that is known about the defendants is that they were arrested last year and that AB has been charged with engaging in preparations for terrorism while CD is accused of improperly possessing a British passport.
Shami Chakrabarti, the director of civil liberties body Liberty, said the case risked setting "a very dangerous precedent".
"It is just not justice," Chakrabarti told the BBC. "The dangers of this kind of process are obvious, in terms of fairness and public confidence in a decent justice system.
"This may be an enormous precedent, but this contagion of secret justice has been spreading through our legal system since before 9/11, and each time the authorities either legislate or apply to the court for further secrecy, we are told this is exceptional.
"Before you know it you wake up one morning and the exceptional has become routine."
Chris Grayling, the justice secretary, said he was "very confident" that judges would be acting in the interests of justice if they decided to hold a major terrorism trial behind closed doors.
"That's why we trust the judges, that's why we have them, to take the right decisions of behalf of all of us."
Sadiq Khan, the the shadow justice secretary, told the Guardian: "A cloak of secrecy on this scale is unprecedented. Open justice isn't some optional add on – transparency and openness are absolutely critical to the way our courts run.
"Deviating from this runs the risk of undermining the public's confidence in justice being done and is a slippery slope."