Adrienne McKellar said she rose to a senior position as human resources advisor in a job previously held by a man though his title was human resources superintendent.
Despite performing identical duties as the man who retired, McKellar said she was paid $35,000 less per year at the mill operated by Zellstoff Celgar Ltd.
McKellar said she complained to her supervisor and to the mill's parent company, Mercer International Inc., which agreed to launch an investigation.
The investigator found no proof of discrimination and McKellar was fired soon after in June 2012.
"She was fired because she had the courage to complain that sex discrimination was going on in that company," said her lawyer Lindsay Lyster.
Three other female supervisors are named in the complaint and also claim they faced discrimination based on gender.
Susan Meredith said she was denied a promotion in favour of a man with less experience.
Christine Galer resigned because she allegedly received less pay and vacation time than subordinate male colleagues, and Diane Perehudoff was allegedly paid $10,000 less a year than a man with less experience.
The mill previously sought to have the complaint dismissed, saying each of the women made substantially different allegations, but the tribunal decided there were enough similarities for the complaint to proceed.
A date for a hearing has not been set.
The tribunal did not make a decision about the merit of the complaint and the allegations have not been proven.
In its response to the complaint, Zellstoff Celgar denied that discrimination occurred. The company said non-unionized salaries are set by an external firm, which evaluates each position with names and references to gender removed.
The mill also said that a woman in one of the two most senior positions at the company is paid the same as her male counterpart.
"The threshold which the tribunal applies to determine whether a complaint should proceed is fairly low," said the company's lawyer, Naz Mitha, who declined to comment further while the matter is before the tribunal.
In McKellar's case, the company said she was given a different title than the man who previously held the position because that individual had vast human resources experience and had worked at the mill for about 20 years.
McKellar joined the company in 2006 and had been working in human resources for about a year.
The company said it responded "promptly and appropriately" to her allegations of discrimination.
However, McKellar said the manager who handled the investigation did not speak to any other women.
Zellstoff Celgar said McKellar was fired because she shared confidential information about employees, including wages, during her discussions with management about the investigation — an allegation she denies.
Her lawyer said the complainants work in a traditionally male-dominated industry, and they want to see conditions improve for other women in manufacturing as well.
"I think it's very courageous of these women to have stood up and to take the risks involved in bringing these kinds of issues out in the public realm," Lyster said.
— By Laura Kane in Vancouver