Tech companies are no stranger to allegations of sexual discrimination. Accusations against Uber contributed to ex-CEO Travis Kalanick stepping down, while AR firm Magic Leap was another firm to be hit with a discrimination lawsuit earlier this year. Now, three women have filed a proposed class-action suit against Google, claiming it is biased against women when it comes to pay and promotions.

The complaint, filed on behalf of all women who worked for Google in California in the last four years, says the company paid women less than men for doing "substantially similar work under similar working conditions," and were less likely to be promoted.

Lead plaintiff Kelly Ellis, who was hired as a software engineer for Google Photos in 2010, said she was placed in a "Level 3" position usually assigned to college graduates. When a male software engineer who graduated alongside Ellis was hired a few weeks later, he was assigned to a "Level 4" position, which came with a better salary, bonuses, raises, and equity.

Holly Pease, another plaintiff, joined Google in 2005 and advanced to a senior management role. Despite overseeing 50 staff across multiple teams and boasting ten years' experience as a network engineer before Google, she was considered to be a "non-technical" employee, which limited her pay. The lawsuit says she was denied the chance to gain the "technical" classification and was moved out of engineering entirely when she returned from medical leave.

The third plaintiff, Kelli Wisuri, came to Google with three years of sales experience but was put in a "level 2" role, the "lowest level available to permanent, full-time employees." The complaint claims men with similar qualifications were place in "Level 3" positions, which have better pay and career tracks. She resigned in 2015 due to "lack of opportunities for advancement for women."

The news comes as the Department of Labor continues to investigate Google over claims of "extreme" gender pay discrimination.

The search giant has released a statement defending itself against the allegations made in the lawsuit.

"We work really hard to create a great workplace for everyone, and to give everyone the chance to thrive here. In relation to this particular lawsuit, we'll review it in detail, but we disagree with the central allegations," spokeswoman Gina Scigliano said. "Job levels and promotions are determined through rigorous hiring and promotion committees, and must pass multiple levels of review, including checks to make sure there is no gender bias in these decisions. And we have extensive systems in place to ensure that we pay fairly. But on all these topics, if we ever see individual discrepancies or problems, we work to fix them, because Google has always sought to be a great employer, for every one of our employees."