WASHINGTON — In a victory for pregnant women in the workplace, the Supreme Court ruled Wednesday in favor of a worker who sued shipping giant UPS for pregnancy discrimination, sending her lawsuit back to a lower court where she had previously lost.

The case, Young v. United Parcel Service, hinged on whether or not UPS was justified in putting Peggy Young on unpaid leave after she became pregnant, even though other workers were commonly offered “light duty” for on-the-job injuries or to satisfy requirements under the American with Disabilities Act. The justices ruled 6-3 in favor of keeping Young’s lawsuit alive, with Chief Justice John Roberts and Justice Samuel Alito joining the traditionally liberal members of the court.

Justice Stephen Breyer, writing for the majority, said the question the lower court needed to ask was “why, when the employer accommodated so many, could it not accommodate pregnant women as well?”

The decision essentially vacates a 2013 ruling by the 4th U.S. Circuit Court of Appeals that threw out Young’s case.

Samuel Bagenstos, a lawyer for Young, called the ruling a “big win” in a tweet shortly after the decision came out.

“The Court recognized that a ruling for UPS would thwart Congress’s intent. It adopted most of our key arguments,” Bagenstos said, in an apparent reference to the Pregnancy Discrimination Act. The 1978 law says that companies cannot treat pregnant workers any differently from other workers who are “similar in their ability or inability to work.”

The question at the heart of the case was whether the Pregnancy Discrimination Act requires companies to offer light-duty options to pregnant workers if they already do so for non-pregnant workers in other situations.

UPS had maintained that its light-duty rules were “pregnancy neutral,” treating a pregnant worker like Young the same as anyone else. Under its collective bargaining agreement with the Teamsters, UPS said it didn’t have to accommodate workers with “off-the-job injuries or conditions,” except for cognitive disabilities under the Americans with Disabilities Act.

The company tried to claim a partial victory after Tuesday’s decision, saying in a statement that the Supreme Court “rejected the argument that UPS’s pregnancy-neutral policy was inherently discriminatory.” UPS said it was “confident” it would prevail in the lower courts, where Young’s case may now go to trial.

Whatever the outcome of Young’s lawsuit, the Supreme Court case has reflected poorly on UPS. Young sued the company in 2008 and lost her case without a trial. That decision was upheld by the 4th Circuit in 2013, leading Young to appeal to the Supreme Court. Last year, not long before oral arguments were set to begin, UPS announced that it was changing its accommodation policy for pregnant workers, after years of defending it in court. As of Jan. 1, 2015, pregnant UPS workers are entitled to light duty.

Young, who was interviewed by The Huffington Post in October, was delivering packages for UPS in Maryland when she became pregnant in 2006. Her doctor recommended she not lift more than 20 pounds for the first 20 weeks of her pregnancy. Although light duty was common for many workers, UPS told Young that such accommodations wouldn’t apply to an “off-the-job” condition, which is how it classified her pregnancy.

“I wanted to work,” Young told HuffPost. “I all but begged for them to let me work.”

Young received support for her lawsuit from across the ideological spectrum, with 23 anti-abortion groups lining up behind her alongside the American Civil Liberties Union and the U.S. Women’s Chamber of Commerce. As the anti-abortion coalition noted in its brief, “economic pressure is a significant factor in many women’s decision to choose abortion over childbirth.”