By Lawrence Hurley

WASHINGTON (Reuters) - U.S. Supreme Court justices appeared unsure on Wednesday how to decide a case that could determine whether employers must provide accommodations for pregnant workers who may have physical limitations on duties they can perform.

During a one-hour argument before the nine justices, two of the court's three women - Elena Kagan and Ruth Bader Ginsburg - showed most sympathy for former UPS Inc truck driver Peggy Young. But it was unclear how some of the other justices would vote in the closely watched case involving women's workplace rights.

The case concerns whether the package delivery company violated a federal law, the Pregnancy Discrimination Act, by denying Young's request for temporary changes in work duties after she became pregnant in 2006.

Young, who worked at a Maryland facility, had acted on a midwife's advice that she not be required to lift packages weighing more than 20 pounds (9 kg).

Kagan said UPS's policy allowed non-pregnant workers to seek temporary changes to their job duties in other circumstances without giving pregnant women the same accommodation.

She pressed UPS's lawyer, Caitlin Halligan, on whether the company's interpretation of the law was at odds with the statute's intent to ensure pregnant women are treated fairly.

"What you are saying is that there's a policy that accommodates some workers but puts all pregnant women on one side of the line," Kagan told Halligan.

Although the court's conservatives did not give clear indications how they would vote, Justices Antonin Scalia and Samuel Alito asked questions that signaled some support for UPS.

Scalia said under Young's interpretation of the law, pregnant women could have "most favored nation" status, enjoying benefits employers reserve for only a small number of employees such as senior executives who get driven to work.

One obstacle to deciding the case is that the two sides disagree over whether UPS agreed to accommodate non-pregnant workers requesting light-duty assignments. That prompted Justice Stephen Breyer to wonder whether the case should be sent back to lower courts for further proceedings.

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A federal district court judge and an appeals court have ruled in favor of UPS, which is backed by business groups.

UPS said in October that starting in January it will provide accommodations for pregnant women. The U.S. Equal Employment Opportunity Commission in July issued enforcement guidance saying employers must offer accommodations to pregnant women just as they do for workers with similar physical limitations.

A ruling is due by the end of June.

The case is Young v. UPS, U.S. Supreme Court, No. 12-1226.

(Reporting by Lawrence Hurley; Editing by Will Dunham)