An Ontario judge has ruled a woman must remove her niqab to testify in a Toronto sexual assault case.

Justice Norris Weisman announced his decision after applying a new test set out by the Supreme Court of Canada dealing with witnesses wearing a veil. The woman at the centre of the case is known only as N.S.

"I conclude that to permit N.S. to testify at the preliminary inquiry with her face obscured by the niqab will impair defence counsels' ability to assess her demeanour, as well as the [judge's] ability to assess her credibility," Weisman said.

The woman has been fighting for six years for the right to wear her niqab during the trial of her uncle and cousin, who are accused of sexually assaulting her when she was a child in the 1980s.

Weisman had first ruled in 2008 that N.S. must remove her niqab during testimony. That decision was appealed all the way up to Supreme Court.

The test set out by Canada's top court in December includes four issues a judge must consider, including: the potential witness's depth of religious belief, and whether the veil could lessen the fairness of the trial.

The preliminary hearing for the two relatives accused of sexually abusing the woman is scheduled to begin next week, but her lawyer said the ruling on the niqab will be appealed.

About to turn 75, Judge Weisman is set to retire on May 1.

With files from Laura Lynch