Three women who used to work at Google have filed a lawsuit against the technology giant, alleging it pays women less than men for comparable work.

The suit says Google is aware of the situation, but has not moved to fix it.

It comes as companies in Silicon Valley face growing scrutiny over gender relations.

Google is also under investigation by the US Department of Labour over its pay practices.

"It is time to stop ignoring these issues in tech," said Kelly Ellis, a former software engineer at Google and one of the women who filed the suit.

She posted on Twitter that she hopes the suit will force Google and other companies to change their practices.

My hopes for the Google suit: to force not only Google, but other companies to change their practices and compensate EVERYONE fairly.

— Kelly Ellis (@justkelly_ok) September 14, 2017

The lawsuit, filed in a San Francisco court, says Google discriminates against female staff with lower pay, more limited promotion, and fewer advancement opportunities compared to men with comparable qualifications.

Ms Ellis, for example, was hired in 2010 at a level typically assigned to college graduates, although she had four years of experience, according to the lawsuit. A male colleague with similar levels of experience started on a higher rung.

She was also assigned to a less prestigious engineering role, the suit says

Ms Ellis resigned from Google four years later "because of the sexist culture", the lawsuit said.

Previous allegations

The complaint is seeking class-action status that would cover women working at the company in California for the last four years. They are looking for unpaid wages, among other remedies.

Google said it would review the lawsuit but disagreed with the "central allegations".

"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," spokeswoman Gina Scigliano said in a statement.

Like other companies in Silicon Valley, the company has faced questions about how it treats women before.

About 70% of Google's workforce are men, according to the company. Men represent about 80% of staff in "tech" roles and 75% of leadership positions.

The Department of Labour found systematic pay disparities at the firm during a 2015 audit, according to the lawsuit. The government in January sued Google to get access to more information to see if the patterns held true across a more extensive probe.

A spreadsheet with data from 1,200 employees also found disparities, the New York Times recently reported.

Google also made headlines earlier this summer, when a memo written by a senior Google employee that criticised diversity programmes and hiring practices became public.

Google later fired him.