Discrimination against female workers who might get pregnant in the future, or have been pregnant in the past, is against the law, the Equal Employment Opportunity Commission said this week. For the first time in 30 years, the agency has updated its rules against pregnancy discrimination.

The agency clarified several policies, including one that spells out when businesses may have to provide pregnant workers light duty and another that bans employers from forcing a pregnant worker to take leave even in cases when she's able to continue on the job.

The policy also clarifies that lactation is a pregnancy-related medical condition and so has all the protections of the law, including requirements for schedule flexibility and a private place to express milk.

On the subject of caregivers, the EEOC stated that employers who allow parental leave must provide it to men and women equally.

"If, for example, an employer extends leave to new mothers beyond the period of recuperation from childbirth, it cannot lawfully refuse to provide an equivalent amount of leave to new fathers for the same purpose," the agency said in a Q&A on its rules.

The update comes some 40 years after the Supreme Court ruled that pregnancy didn't constitute a sex-based classification — a decision that helped prompt Congress to pass the Pregnancy Discrimination Act in 1978.

Interpretations of that law, as well as portions of the Americans with Disabilities Act, have varied widely, a situation that has led to complaints and lawsuits.

"The latest EEOC data show a 46 percent increase in pregnancy-related complaints to the EEOC from 1997 to 2011," the AP reports.

The Supreme Court recently agreed to hear the case of a UPS worker who was forced to take unpaid leave after she became pregnant.

As NPR's Yuki Noguchi reported about that case, the plaintiff had been seeking an alternative assignment like those that her bosses had given people with conditions such as high blood pressure. Instead, the woman says she was told the company didn't make allowances for "off-work incidents."

Many employers have been uncertain about the federal law's requirements and how they apply. With its new rules, the EEOC is hoping to provide more clarity.

In announcing the new guidance, EEOC Chair Jacqueline A. Berrien said:

"Pregnancy is not a justification for excluding women from jobs that they are qualified to perform, and it cannot be a basis for denying employment or treating women less favorably than co-workers similar in their ability or inability to work. Despite much progress, we continue to see a significant number of charges alleging pregnancy discrimination, and our investigations have revealed the persistence of overt pregnancy discrimination, as well as the emergence of more subtle discriminatory practices."

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