The Equal Employment Opportunity Commission's update makes it clear that any form of workplace discrimination or harassment of pregnant women by employers is illegal.
The guidelines were last updated in 1983. The issue has gained increasing attention as the Obama administration ratchets up its enforcement of the nation's anti-discrimination laws.
The American Civil Liberties Union welcomed the update, saying pregnancy should not be used to justify excluding women from jobs. But it was opposed by some Republicans, including those on the five-member commission.