Massachusetts Medical Society
Employers have historically limited women's access to traditionally male, high-paying jobs. In one famous case early in this century, the U.S. Supreme Court upheld an Oregon law that forbade hiring women for jobs that required more than 10 hours of work a day in factories. The Chief Justice explained that this restriction was reasonable because "healthy mothers are essential to vigorous offspring" and preserving the physical well-being of women helps "preserve the strength and vigor of the race." This rationale was never particularly persuasive, and women's hours have not been limited in traditionally female, low-paid fields of employment, such as nursing. Although such blatant sex discrimination in employment is a thing of the past, the average man continues to earn "almost 50 percent more per hour than does the average woman of the same race, age, and education.
George J. Annas,
Fetal Protection and Employment Discrimination - The Johnson Controls Case
New England Journal of Medicine
Available at: https://scholarship.law.bu.edu/faculty_scholarship/1245