Thousands of women were systematically underpaid at Oracle, one of Silicon Valley’s largest corporations, according to a new motion in a class-action complaint that details claims of pervasive wage discrimination.

A motion filed in California on Friday said attorneys seek to represent more than 4,200 women and alleged that female employees were paid on average $13,000 less per year than men doing similar work. An analysis of payroll data found disparities with an “extraordinarily high degree of statistical significance”, the complaint said. Women made 3.8% less in base salaries on average than men in the same job categories, 13.2% less in bonuses, and 33.1% less in stock value, it alleges.

The civil rights suit comes as the tech industries faces increased scrutiny of gender and racial discrimination, including sexual misconduct, unequal pay and biased workplaces. The case against Oracle, which is headquartered in Redwood Shores and provides cloud computing services to companies across the globe, resembles high-profile litigation against Google, which has also faced repeated claims of systematic wage discrimination.

“I just couldn’t believe it. I was angry,” Marilyn Clark, one of the Oracle plaintiffs, told the Guardian. The complaint alleged that she discovered the wage gap when she saw a pay stub a male colleague had left in a common area. “I felt like I had been punched in the gut.”

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Clark, 66, who has since retired from Oracle, said it was particularly painful because she had even trained the male employee, who was making roughly $20,000 more than she was, amounting to a 22% higher salary.

“Women are getting paid less across the board,” said Jim Finberg, attorney for the plaintiffs. “These are some of the strongest statistics I’ve ever seen – amazingly powerful numbers.”

The proposed class includes women who have worked in product development, information technology and support functions since 2013. The huge gaps in base salaries, bonuses and stock value are not justified by any “valid job-related reasons”, the complaint said, noting that the disparities exist even for women and men with the same tenure and performance review score in the same job categories. Women in the same locations and with the same amount of experience also made less than equivalent men, an analysis for the plaintiffs’ found.

“What explains the disparity is being a woman. That is not right and that is not legal, and it’s time for Oracle to change,” said Finberg, who brought a similar case against Google.

Both Oracle and Google have also faced accusations of pay discrimination by the US department of labor (DoL), which is responsible for enforcing equal pay laws for companies that have contracts with the federal government. The DoL filed a suit against Oracle in 2017 alleging that the firm had a “systemic practice” of paying white male workers more than their counterparts in the same job titles, leading to pay discrimination against women and black and Asian employees.

Oracle said at the time that the DoL allegations were “without merit” and that its pay decisions were “non-discriminatory and made based on legitimate business factors including experience and merit”. An Oracle spokesperson declined to comment on the new complaint on Friday.

The class-action complaint, which names six plaintiffs, said some of the women had discovered the pay disparities by chance. Xian Murray, a software engineer, “just happened to be present when her manager complained to other managers that ‘women are paid less in Oracle’,” the complaint said.

I’m doing it for my daughter. I don’t want to see her be discriminated against Marilyn Clark

Clark, who worked in IT and was at Oracle for 10 years before leaving in 2015, said she had initially stayed quiet about the pay gap she discovered: “I just kept it to myself, because we didn’t talk about salary. That’s how I was raised.”

But when she learned it was a widespread problem, Clark said, she decided she wanted to be a part of the case: “I’m doing it for my daughter. I don’t want to see her be discriminated against in the future.”

Part of the reason for the disparities is that Oracle has used the prior salaries of new hires to determine their compensation at the company, which has perpetuated inequalities in pay, the suit said. The state of California has banned employers from asking applicants about prior pay in an effort to curb wage discrimination.

The suit further claimed that Oracle was aware of its discriminatory pay and had failed to close the gap even after the US government alleged specific problems.

“Oracle has decided to take a ‘flexible’ approach to pay equity and not to conduct regular comprehensive internal pay audits,” lawyers wrote in the complaint. “Oracle’s laissez-faire approach failed on a large scale.”

Clark said she hoped the case would inspire reforms at Oracle and other companies, adding: “I’d like to see the women who I worked with getting some kind of compensation for what we missed out on.”

Finberg said none of the named plaintiffs worked at Oracle any more, with some leaving due to their frustrations over discriminatory pay.

“It’s depressing. It’s demoralizing,” he said. “They didn’t want to work in an environment like that.”