Twitter had 22 top engineers, and all of them were men, says an ex-employee in a sex discrimination lawsuit

Former Twitter employee Tina Huang has launched a proposed class-action law suit, claiming her former employer has a complicated promotion system that unfairly favors men over women.

Huang's suit lists a number of complaints, including that Twitter allegedly failed "to promote women on the same basis as men are promoted and compensated" and that Twitter allegedly did not "provide women with accurate and timely notice of promotional opportunities."

The suit also alleges that Twitter's management team had failed "to take adequate steps to eliminate the effects of its past discriminatory practices" and retaliated "against women employees who complain of unequal treatment."

Twitter was one of many tech companies to report its diversity stats last year.

According to Twitter's blog, 70% of the company's global employees are men. 90% of Twitter's technical employees are men.

But Huang's suit alleges that the gender breakdown at Twitter headquarters is even worse than that.

According to the complaint obtained by the San Francisco Chronicle, "a closer look at the software engineering division at the company's headquarters shows an even starker contrast: every member of the top level principal and senior staff engineer positions during Ms. Huang's tenure (about 22 total positions) was a man."

"In Ms. Huang's staff software engineer position, only about seven of 164 employees, or about 4 percent, are women."

Huang worked at Twitter from 2009 to 2014, occupying various software engineering roles during that time. After she complained directly to CEO Dick Costolo that she was repeatedly overlooked for promotions, she alleges, she was put on leave. She eventually resigned.

Huang's lawyers want the suit to include other women who were "denied promotions in the three years prior to the filing of this complaint to Software Engineer II, Senior Software Engineer, Staff Software Engineer, Senior Staff Software Engineer, or similarly titled positions in California," the Chronicle reports.

A Twitter spokesperson provided this statement to Business Insider: "Ms. Huang resigned voluntarily from Twitter, after our leadership tried to persuade her to stay. She was not fired. Twitter is deeply committed to a diverse and supportive workplace, and we believe the facts will show Ms. Huang was treated fairly.