Ms. Ledbetter lost her case because she had discovered the disparity between her pay and that of her male colleagues too late.
The later effects of past discrimination, the court ruled last year in Ledbetter v. Goodyear Tire and Rubber Company, a 5-to-4 decision, do not restart the clock on the statute of limitations. President-elect Barack Obama has supported efforts to overturn that decision in Congress.
The case that was argued Wednesday, AT&T v. Hulteen, No. 07-543, raised broadly similar issues. Noreen Hulteen and three other women took pregnancy leaves from AT&T from 1968 to 1976. When the company calculated their pension benefits on their retirements decades later, it did not give them full credit for the leaves.
The women and their union sued under the Pregnancy Discrimination Act of 1978, which made discrimination based on pregnancy-related conditions a form of sex discrimination.
AT&T responded with two arguments. One was that it had done nothing wrong by treating pregnancy leaves differently from other kinds of leave before the 1978 law was enacted. Its discriminatory conduct was lawful when it occurred, the company said. And its later reliance on that conduct in calculating benefits did not turn that lawful conduct into illegal discrimination.
If it had done something wrong, the company went on, the plaintiffs should have sued long ago, and they would be barred by the statute of limitations from suing now.
That was, the company said, consistent with Justice Samuel A. Alito Jr.’s opinion for the majority in the Ledbetter case. “Current effects alone,” Justice Alito wrote last year, “cannot breathe life into prior, uncharged discrimination.”
Justice Ruth Bader Ginsburg, who dissented in the Ledbetter case, appeared unpersuaded on Wednesday. The plaintiffs would have had no reason to sue when they returned from their pregnancy leaves, she said. “Nothing had happened to them,” she said, “except there was a bookkeeping entry.”
Carter G. Phillips, representing AT&T, said that immediate seniority determinations also turned on how leaves were calculated. “That’s an actionable claim,” he said, one that should have been pursued at the time and is no longer available.
Ledbetter was the culmination of a line of cases helpful to the company. But several justices said another case, Bazemore v. Friday in 1986, might be a better fit. There, Justice William J. Brennan Jr. said that previously lawful pay discrimination based on race could not be used as the baseline for pay after the enactment of the Civil Rights Act of 1964.
“Each week’s paycheck that delivers less to a black than to a similarly situated white is a wrong actionable under Title VII” of the 1964 law, Justice Brennan wrote, “regardless of the fact that this pattern was begun prior to the effective date of Title VII.”
Justice David H. Souter said the Bazemore decision might provide a good analogy. “Why can’t you make exactly the same kind of analysis here?” he asked. “Why isn’t the payment of the retirement benefit exactly on par with the payment of the salary in Bazemore?”
In response, Mr. Phillips said, “That’s certainly not an implausible way of trying to look at this.” But he said that the Ledbetter decision was a closer fit.
The Equal Employment Opportunity Commission supported the plaintiffs in the Hulteen case in the United States Court of Appeals for the Ninth Circuit in San Francisco, which ruled in their favor. But the federal government appeared on behalf of the company on Wednesday.
Members of the commission “are taking a position that is 180 degrees opposite yours,” Justice Ginsburg said to Lisa S. Blatt, an assistant attorney general.
Ms. Blatt said that was “absolutely correct” and that the Ledbetter decision had explained that the commission’s views on the interpretation of Supreme Court precedents are “entitled to no special deference.”
Kevin Russell, representing the plaintiffs, said his clients “weren’t required to challenge this discrimination” when it happened “because it wasn’t a completed, unlawful employment practice at the time.”
“At the time that these leaves are taken typically,” he added, “the person is years away, perhaps decades away, from even vesting in their benefits pension.”