WASHINGTON - Peggy Young only has to look at her younger daughter to be reminded how long she has fought United Parcel Service over its treatment of pregnant employees, and why.

Young was pregnant with Triniti, who's now 7 years old, when UPS told Young that she could not have a temporary assignment to avoid lifting heavy packages, as her doctor had ordered.

"They told me basically to go home and come back when I was no longer pregnant," Young said in an interview with The Associated Press. "I couldn't believe it."

She sued the Atlanta-based package-delivery company for discriminating against pregnant women. She lost two rounds in lower courts, but the Supreme Court will hear her case Wednesday.

The 42-year-old Young, who lives in Lorton, Va., said her persistence is not only for herself. "I am fighting for my two daughters and I'm fighting for women who want to start a family and provide for the family at the same time," she said.

UPS spokeswoman Kara Gerhardt Ross said the law is on the company's side. "UPS did not intentionally discriminate," Ross said.

The outcome could have wide-ranging effects.

Three-quarters of women entering the workforce today will become pregnant at least once while employed, and many will work throughout their pregnancies, employment discrimination expert Katherine Kimpel wrote in a court brief. Some will experience complications or physical effects that cause them to ask their employers for a change of duties or other modifications, Kimpel said.

Young's case hinges on the Pregnancy Discrimination Act, a law that Congress passed in 1978 specifically to include discrimination against pregnant women as a violation of the 1964 Civil Rights Act. Congress acted after the Supreme Court, then composed entirely of men, said workplace rules that excluded pregnant workers from disability benefits and insurance coverage did not amount to sex discrimination under the landmark civil rights law.

The question in Young's case is whether UPS violated the law through its policy of providing temporary light-duty work only to employees who had on-the-job injuries, were disabled under federal law or lost their federal driver certification.

"If you were painting your house and fell off a ladder, or if you had a ski accident, that wouldn't qualify for restricted light duty. That's where pregnancy fell at that time. It was not covered in any state law except California's," Ross said.

UPS also notes in its court filings that the Postal Service, an independent agency that receives no tax dollars but is subject to congressional control, maintains an identical policy when it comes to pregnant workers. The Postal Service declined comment.

The Obama administration and 120 congressional Democrats are supporting Young. The reason for the work limitation is less important than the company's decision to distinguish between pregnant and nonpregnant workers with similar restrictions on the work they can do, Young and the administration told the court.

An unusual array of liberal, conservative, labor and women's interest groups also has lined up behind Young. The pregnancy discrimination law "protects the unborn child as well as the working mother who faces economic and other difficulties in bearing and raising the child," lawyer Carrie Severino wrote on behalf of anti-abortion organizations.

UPS employed Young as a part-time driver whose main job was to deliver overnight letters by 8:30 a.m. UPS requires people in those jobs to be able to lift packages as heavy as 70 pounds. Young said she rarely handled anything over 20 pounds and dealt almost exclusively with letters that sat on the passenger seat of her van.

In 2006, Young, then in her mid-30s, took a leave of absence to undergo in vitro fertilization in her desire to have a third child. On the third try, she became pregnant.

Young wanted to return to work, and her doctor and a midwife wrote notes saying she should not lift packages heavier than 20 pounds.

But UPS told Young she could not continue in her job and did not qualify for a temporary assignment.

Unable to work, Young also lost her medical and pension benefits, although she was covered under husband's health insurance. "The benefits were good and benefits were hard to find with part-time jobs," she said.

Young eventually returned to UPS, but left in 2009, a year after she sued. She argued that because UPS made accommodations for nonpregnant employees with work restrictions, it should have done the same for her.

But lower courts dismissed the suit, agreeing that Young did not prove UPS discriminated against her because of her pregnancy.

The justices agreed in July to review the case. Since then, there have been two notable developments.

The Equal Employment Opportunity Commission updated guidance to employers to make clear that they should accommodate people in Young's situation.

UPS itself has changed its policy so that pregnant employees will be eligible for light-duty work. "UPS believed it was appropriate to update its workplace policies so that we can attract and retain the best workforce we can," Ross said.