McCarthy Tetrault has been hit with a court order to produce reams of confidential financial data after a former employee accused the firm of routinely discriminating against female staff.

McCarthy, Canada's largest law firm, is facing a 7 September deadline to come forward with information about partner, associate and staff compensation.

The court order stems from a sexual discrimination suit filed by former partner Diana LaCalamita against the 650-lawyer firm in April 2008.

The order is believed to be the first time that a major Canadian firm has been ordered to provide data disclosing salaries, billing rates, performance reviews, and other secret firm information.

LaCalamita, a former intellectual property partner at the firm, was laid off in mid-2006 and offered $185,500 (£114,000).

LaCalamita refused the settlement offer and sued the firm in Ontario Superior Court for $11.1m (£6.8m), claiming that McCarthy discriminated against her when it denied her equity partnership after recruiting her from Toronto firm Aird & Berlis in 2003.

LaCalamita also accused McCarthy of routinely billing out female partners at lower rates than men and boosting its bottom line by paying women lower salaries.

Since being fired by McCarthy, LaCalamita has been unable to find work as a lawyer. She has turned to prominent Canadian constitutional lawyer Mary Eberts and Malcolm MacKillop, a name partner with Toronto labour and employment boutique Shields O'Donnell MacKillop, to represent her.

McCarthy is being advised by Terrence O'Sullivan from Toronto's Lax O'Sullivan Scott. The firm has vigorously denied LaCalamita's accusations, including that systemic gender-based discrimination occurs against other female lawyers, asserting that her firing was entirely performance-based.

However, the Ontario court has already allowed LaCalamita to have access to an internal report on women's issues at the firm prepared by Catalyst, a consultant that advises on feminist issues in the workplace. McCarthy commissioned the report as part of an in-house investigation of gender issues.

McCarthy will now also turn over detailed statistics for the 2003-06 period when LaCalamita worked at the firm for the following: billable hours for members of the IP group, the compensation structure for income and equity partners, and the male-female ratio among the firm's equity partnership.

This article first appeared on The Am Law Daily blog on americanlawyer.com.