A judge said that if a Muslim woman refuses to take off her veil in court to give evidence she should not be allowed to testify.
The woman must also remove her niqab in front of a female police officer or other witnesses for identification purposes.
Judge Peter Murphy said the woman must be given time to reflect when asked to take off her veil and added: "If she refuses the judge should not allow her to give evidence and must give the jury a clear direction."
He also said: "No tradition or practice, whether religious or otherwise, can claim to occupy such a privileged position that the rule of law, open justice and the adversarial trial process are sacrificed to accommodate it.
"That is not a discrimination against religion, it is a matter of upholding the rule of law in a democratic society."
A judge ruled that it was "crucial" for a Muslim woman to remove her veil when giving evidence in court.
Judge Peter Murphy was giving his final judgement at Blackfriars Crown Court on whether a 22-year-old woman from London, who cannot be identified for legal reasons, could hide her face with a niqab veil when giving evidence.
He said: "The ability of the jury to see the defendant for the purposes of evaluating her evidence is crucial."
The judge said he "expresses the hope that Parliament or a higher court will provide a definite answer" to the issue soon, adding: "The niqab has become the elephant in the court room."
A judge will decide today whether a Muslim woman should be allowed to stand trial while wearing a full-face veil.
Judge Peter Murphy is due to hand down written directions about whether the defendant, who says it is against her religious beliefs to show her face in public, will have to allow the jury and other people in court see her
The 22-year-old from London, who cannot be identified for legal reasons, entered a not guilty plea to a charge of intimidation last week while wearing a niqab after the judge backed down from a previous decision that she would have to show her face to be properly identified.