'In the maternity case, Souter wrote for the majority in overturning a lower court ruling that said the decades-old maternity leaves should count in determining pensions.
Four AT&T employees, including Noreen Hulteen, who took maternity leave between 1968 and 1976, sued the company to get that leave time credited toward their pensions. At the time, the company used to count pregnancy leave as "personal" and said the time out of work did not count toward seniority for pension purposes.
But it was not until 1979 that the Pregnancy Discrimination Act, which barred companies from treating pregnancy differently from other disability leaves in determining pensions, went into effect.
"A seniority system does not necessarily violate the statute when it gives current effect to such rules that operated before the PDA," Souter wrote.'
http://www.washingtonpost.com/wp-dyn/content/article/2009/05/18/AR2009051800966_2.html?hpid=topnews&sid=ST2009051801430