The U.S. Supreme Court backed the rights of pregnant workers, reviving a lawsuit by a former United Parcel Service Inc. driver who left her job when the company would not provide the less strenuous work recommended by her doctor.

The justices, voting 6-3, sent the case back for a possible trial, which would center on UPS's reasons for refusing to accommodate Peggy Young's needs while giving temporary assignments to workers recovering from on-the-job injuries.

The ruling is the Supreme Court's first since 1991 on employers' duties toward their pregnant workers. Although it may have limited significance going forward because of legal changes at the state and federal level, the case touched on issues that have driven a wedge through the court and American society.

The justices divided to some degree along ideological lines. The court's three women - Ruth Bader Ginsburg, Sonia Sotomayor, and Elena Kagan - joined Justice Stephen G. Breyer in the majority, as did two Republican appointees, Samuel A. Alito Jr. and Chief Justice John G. Roberts Jr.

Writing for the court, Breyer said the lower court that threw out the suit should have scrutinized UPS's justification for accommodating other workers.

"Why, when the employer accommodated so many, could it not accommodate pregnant workers as well?" Breyer wrote.

The opinion adopted what Kagan characterized during arguments in December as a "middle ground" approach, rejecting more sweeping contentions from both sides. Because lower courts had generally backed employers on the issue, it gives some pregnant workers a new avenue to win cases.

UPS, which has a large operation at Philadelphia International Airport, contended that the Pregnancy Discrimination Act leaves room for companies to have neutral policies like seniority systems and special preferences for workers who are injured on the job.

"UPS is pleased that the Supreme Court rejected the argument that UPS's pregnancy-neutral policy was inherently discriminatory," the company said in a statement. The company said it was confident the lower courts "will find that UPS did not discriminate against Ms. Young under this newly announced standard."

Alito did not join Breyer's reasoning, writing separately to explain his views.

In dissent, Justice Antonin Scalia said the majority departed from the Pregnancy Discrimination Act's text.

"The court seems to think our task is to craft a policy-driven compromise between the possible readings of the law, like a congressional conference committee reconciling House and Senate versions of a bill," Scalia wrote.

Young worked at a UPS facility in Landover, Md. Her job required her to load packages onto vehicles and deliver them to their destination. Although she says the vast majority of those packages were envelope-sized, her job description required her to lift parcels of up to 70 pounds.

In 2006, Young became pregnant after in vitro fertilization. Her doctor and midwife said she should not lift objects weighing more than 20 pounds during the first half of the pregnancy or more than 10 pounds for the rest.

She says UPS refused to accommodate her needs either by adjusting her job responsibilities or by temporarily assigning her to a position that didn't require heavy lifting.

She went on an unpaid leave of absence and returned to work after her baby was born. Young later left UPS and sued the company for compensation.

UPS says it was simply abiding by its seniority system and union contract, which makes no provision for pregnant employees with physical limitations. The union agreement called for reassignments to be available to workers with job-related injuries and those considered permanently disabled under the Americans With Disabilities Act. The accord also made provisions for people who lost their federal driver's certification, letting them temporarily take jobs that don't involve operating a vehicle.

Atlanta-based UPS shifted its policy after the Supreme Court agreed to hear the case, Young v. UPS. UPS says it now treats pregnant employees in need of special accommodations the same as workers with on-the-job injuries, giving them light-duty assignments if available. Young, now 43, continued to press her case in an effort to win damages.