I believe in equal pay for equal work, but...
Where I used to work we hired two additional software engineers right out of college, Duane and Sandy, on the same day. Both had Master’s Degrees. After 5 years Sandy found out that Duane was making more than she was and filed a complaint that she should make as much as Duane, i.e., hired the same day with similar qualifications, 5 years later..
But in those 5 years Sandy had taken two 9-month leaves of absence when her children were born. After the 5 years Duane had 60 months of work experience while Sandy had only 42 months of work experience.