Further details have been suppressed by the tribunal.
The charges against the lawyer, who has a current practising certificate, will be heard in Wellington during May.
The decision also ruled on the Committee seeking to introduce hearsay evidence for one of the charges after the complainant is said to have spoken about the incident to four other women and one man "in close proximity to the alleged event".
The Committee wanted to include the accounts of the five confidants because the complainant has not shown any inclination to involve herself in this disciplinary process and never made a written statement to the Law Society.
"Indeed, she has, through her barrister, Maria Dew QC, expressed an overt desire not to participate," the decision reads.
However, the tribunal, chaired by Judge Dale Clarkson, ruled the hearsay evidence inadmissible.
"In this case, while we have considerable sympathy for the alleged victim's position, there is no 'compelling reason' why she should be 'exempted from giving evidence'.
"Sadly, there are many cases of sexual abuse that are heard throughout the country every day and, despite the obvious trauma caused to victims, they are expected to give evidence to support the allegations of fact made against an accused person."
The tribunal said it was also concerned about "the nuanced differences" in the statements said to have been relayed to the five confidants by the complainant.
"Two of the five confidants do not state precisely what they were told but express their own conclusions about what happened. Evidence such as that could not be admitted on any basis," the decision reads.
In July 2018, Dame Margaret Bazley released an independent review into Russell McVeagh and made several recommendations for the law firm after allegations surfaced of clerks being sexually harassed over the summer of 2015-16.
She found junior lawyers and staff were encouraged to "drink to excess" during that period, in a "work hard, play hard" culture which had instances of crude and sexually inappropriate behaviour.
Bazley noted failings in the firm's governance and policies, including no code of conduct, which she said contributed to poor management of the incidents.
A Law Society working group, chaired by Dame Silvia Cartwright, was also established in April 2018 following widespread allegations of sexual harassment, bullying and discrimination within the legal profession.
Its report, released in December 2018, found female lawyers have been subjected to "sexual objectification" for decades.
A confidential online survey of lawyers by the Law Society in 2018 also showed about one in three female lawyers have been sexually harassed at some time during their career.
