Sen. Elizabeth Warren’s story about being fired early in her career because she was pregnant may sound like an artifact from a less enlightened era, but pregnancy-discrimination cases are not uncommon in Corporate America today.

Warren — a Democrat from Massachusetts who’s vying for the Democratic nomination — told CBS News that she was fired for being pregnant in 1971. She then urged other women to share their stories of pregnancy discrimination on Twitter TWTR, +1.62% .

“This was 1971, years before Congress outlawed pregnancy discrimination — but we know it still happens in subtle and not-so-subtle ways,” she wrote.

The Pregnancy Discrimination Act passed in 1978, but more than 40 years later discrimination against pregnant workers is still “incredibly common,” said Alex Baptiste, policy counsel at the National Partnership for Women & Families, an organization that advocates for adequate health care, reproductive rights, equal pay and family-friendly policies. The U.S. Equal Employment Opportunity Commission fielded more than 2,000 complaints of pregnancy discrimination in 2018.

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“It impacts people across industry, pay scale, race, ethnicity, background — it can happen in any work environment and in any state,” Baptiste said.

Some of the country’s biggest employers, including Walmart WMT, +0.41% and UPS UPS, +3.56% , have been the focus of pregnancy-discrimination complaints, and a 2018 New York Times investigation explored its presence across sectors, from financial firms to factory floors.

A report in the Washington Free Beacon, a conservative publication, questioned Warren’s account, citing the minutes of a Riverdale Board of Education meeting on April 21, 1971. Hundreds of women on social media subsequently shared their own stories of more subtle forms of discrimination, and being forced out and also frozen out by an organization when managers discovered they were pregnant.

Warren, meanwhile, said she didn’t previously share the details of her exit from that teaching post, telling CBS News: “After becoming a public figure I opened up more about different pieces in my life, and this was one of them. I wrote about it in my book when I became a U.S. senator.”

Pregnancy discrimination can be as overt as an employer firing a worker when they find out she’s pregnant, but it also includes less explicit forms of unfair treatment, like not letting a pregnant worker have a water bottle near her work area, Baptiste said. “All of these things have real consequences and affect a pregnant worker’s employment, earnings and opportunity,” she added.

The changing demographics of the American workforce are one factor in the persistence of this type of discrimination.

“Over the last several years, as more women entered the workforce, and have moved into more occupations or industries that were previously male dominated, there’s been an increase in denial of requests for accommodations for pregnant workers, and firing them for doing so,” said Maya Raghu, director of workplace equality and senior counsel at the National Women’s Law Center, an organization that supports advocates, experts, and lawyers who work for gender equality in the workplace.

What’s more, women are far more likely to work while they’re pregnant than in decades past, and they tend to work until they are further along in their pregnancies, a 2015 Pew Research Center analysis found.

The NWLC filed a class-action lawsuit in 2017 against Walmart on behalf of pregnant workers, one of whom said the company denied her request to not lift heavy objects or climb ladders while pregnant. The EEOC filed a similar suit against the mega-retailer in 2018. Both suits are ongoing. Walmart did not respond immediately to a request for comment.

The EEOC has brought several pregnancy-discrimination cases recently against employers:

• UPS, which lost a pregnancy-discrimination case before the U.S. Supreme Court in 2015, paid a $2.25 million settlement in September to settle charges that it did not provide light duty accommodations to pregnant workers. A UPS spokesman told MarketWatch, “UPS works closely with our female employees to make their work experience a positive one throughout their pregnancies, the births of their children, and caring for related medical conditions. Our maternity leave benefits have included paid time off and opportunities for light duty work assignments for several years.”

• EEOC sued Tacoma, Washington’s Oatridge Security in September after a supervisor allegedly told a pregnant worker that working security “wasn’t proper” for a pregnant woman. The company did not respond immediately to a request for comment.

• Chain retailer Party City PRTY, +4.46% paid a $39,000 settlement in July after the company allegedly fired a Texas worker because she was pregnant. The company did not respond to a request for comment.

Advocates are now pushing for stronger protections for pregnant workers and want Congress to pass a new law called the Pregnant Workers Fairness Act.

The 1978 Pregnancy Discrimination Act went a long way in providing protections for pregnant workers, but there are still “major holes” in protections for millions of employees, Baptiste said. “The Pregnant Workers Fairness Act would close that protection gap, make reasonable accommodations available to pregnant workers when requested, and allow more pregnant workers to remain in the workforce at a time when the income and benefits are most needed.”