The federal government issued new rules Tuesday protecting mothers, and mothers-to-be, against employer discrimination over pregnancies.

The new Equal Employment Opportunity Commission rules, last updated 30 years ago, say an employer may not discriminate on the basis of pregnancy, childbirth or related medical conditions.

"Pregnancy is not a justification for excluding women from jobs 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," said Jacqueline A. Berrien, Chair of the EEOC, in a statement on the new guidelines.

The new rules under the Pregnancy Discrimination Act say, "An employer cannot fire, refuse to hire, or demote, or take any other adverse action against a woman if pregnancy, childbirth or a related medical condition," is the reason.

An employer may not fire a woman after pregnancy or fire a woman who is considering becoming pregnant, and it's illegal for an employer to discriminate "against an employee because of her breastfeeding schedule."

The updated rules of the PDA, followed a public meeting held in February 2012 by the Commission, which invited participants to give testimony on pregnancy and caregiver discrimination. The public was given 15 days to comment on the meeting record.

One of those participants who gave testimony at the public meeting was Judith L. Lichtman, senior adviser for National Partnership for Women and Families, a nonprofit, nonpartisan advocacy group promoting fairness in the workplace.

Lichtman said, "[W]omen now make up 47 percent of the workforce. As the number of working women has increased, their incomes have become increasingly important to their families economic security. Women are primary or co-breadwinners in nearly two-thirds of families, meaning that a woman's loss of income during pregnancy or leave to care for a newborn has significant consequences for her family. The number of single-parent families also has grown. Single mothers generally bare sole responsibility for the economic security of their families.

She also testified, "Over the past decade, the number of pregnancy charges has increased by 35 percent. About one in five of discrimination cases filed by women involves claims of pregnancy discrimination."

The rules are issued as the Supreme Court has agreed to take up a case of discrimination against a pregnant UPS employee who requested a lighter work load and was told to take unpaid leave instead. The Supreme Court will hear the case in the fall of this year.

"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." said Jacqueline A. Berrien, an EEOC chair.

The EEOC has filed 260 pregnancy discrimination lawsuits against employers over the past decade.