Twitter is the latest Silicon Valley giant to be hit with accusations of gender discrimination, with a former employee claiming the company's policies systematically hold women down.

Tina Huang filed the suit on Friday, the day before the ninth anniversary of the first tweet ever, and claims in the document that Twitter uses what The Verge describes as a "black box" system for job promotions. Instead of formal listings and application processes for job promotions, advancements are decided by a predominantly-male leadership in secret and employees are notified by essentially a shoulder tap. "These judgments are tainted with conscious or unconscious prejudices and gender-based stereotypes, which explains why so few women employees at Twitter advance to senior and leadership positions," the suit reads.

Huang seeks to make the the lawsuit a class-action, reports Pando Daily, saying that Twitter creates a "glass ceiling" for all female engineers at the company that isn't "justified by any reasonable business purpose."

The former engineer also claims that she was forced out five years of employment at the company when she wrote an email to CEO Dick Costolo complaining about the discriminatory promotion process. She was put on leave for three months after the initial complaint and felt forced to resign in May of last year. "Ms. Huang resigned voluntarily from Twitter, after our leadership tried to persuade her to stay. She was not fired," a spokesman for the company told Mashable.

Huang's lawsuit details specifically how these policies prevent women from advancing within Twitter, saying that they are "failing and refusing to consider women for promotion on the same basis as men are considered" and are also "failing to provide women with accurate and timely notice of promotional opportunities." This has kept Twitter's technical workforce at 10%, and is further reinforced with a lack of women in leadership positions. Only one woman sits on their board of directors.

"Twitter is deeply committed to a diverse and supportive workplace, and we believe the facts will show Ms. Huang was treated fairly," said the company.