For the first time in 30 years, the federal government is issuing new guidelines designed to protect pregnant workers from on-the-job discrimination.

The Equal Employment Opportunity Commission (EEOC) update makes it clear that any form of workplace discrimination or harassment against pregnant women by employers is illegal.

“Discrimination based on pregnancy, childbirth or related medical conditions is a prohibited form of sex discrimination,” it said.

The updated guidelines come two weeks after the Supreme Court took under consideration a dispute over the EEOC’s duty to try and settle charges of job discrimination before filing lawsuits against employers.

The issue has gained increasing attention and has vexed business groups as the Obama administration ratchets up its enforcement of the nation’s anti-discrimination laws.

“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,” EEOC chairwoman Jacqueline A. Berrien said in a statement.

The guidelines were last updated in 1983. The newly revised policy spells out for the first time how the Americans with Disabilities Act (ADA), as amended in 2008, might apply to workers with impairments related to pregnancy. And it emphasizes that any discrimination against women workers based on past or prospective future pregnancies is also illegal.

The EEOC issued the new guidelines on Monday.

The American Civil Liberties Union (ACLU) welcomed the update, saying Tuesday that it clarifies employers’ obligations under the Pregnancy Discrimination Act of 1978 and the ADA.

“Far too many pregnant workers have been forced off the job and denied a paycheck just when they need it most, despite the fact that they are willing and able to come to work,” said Laura W. Murphy, director of ACLU’s Washington Legislative Office. “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.”

Debra L. Ness, president of the National Partnership for Women and Families, also praised the updated guidelines as “a much-needed interpretation of the nation’s laws banning discrimination based on pregnancy.”

“By clarifying existing legal protections and defining best practices for businesses in complying with these laws, this new guidance is a powerful tool in the effort to eradicate the unlawful and unequal treatment of pregnant women in the workplace,” Ness said.

“This is a significant victory,” said Joan C. Williams, a law professor at the University of California’s Hastings School of Law in San Francisco. “Too often today pregnant workers lose their jobs when employers deny them accommodations that are regularly granted to other employees.”

But the move drew opposition from some Republicans, including the two GOP members of the five-member commission.