But union and women's rights organizations say it also reflects outright discrimination. Complicating the issue is a phenomenon in the white-collar workplace called the glass ceiling, an invisible barrier that some women say holds them back from promotion to male-dominated executive or professional ranks. In recent years, women have obtained such jobs in growing numbers, but they still lag significantly considering their proportion of the population. Similar issues arise with the pay and positions earned by members of various ethnic and racial groups, often referred to as "minorities" since they make up a minority of the general population. (At the end of the 20th century, the majority of Americans were Caucasians of European descent, although their percentage of the population was dropping.) In addition to nondiscrimination laws, the federal government and many states adopted "affirmative action" laws in the 1960s and 1970s that required employers to give a preference in hiring to minorities in certain circumstances. Advocates said minorities should be favored in order to rectify years of past discrimination against them. But the idea proved a contentious way of addressing racial and ethnic problems. Critics complained that "reverse discrimination" was both unfair and counterproductive. Some states, notably California, abandoned affirmative action policies in the 1990s. Still, pay gaps and widely varying unemployment rates between whites and minorities persist. Along with issues about a woman's place in the work force, 102