Final answer:
The Equal Pay Act of 1963 prohibits wage discrimination based on sex, thereby making it illegal to pay different wages to men and women doing the same work, under similar conditions. Other forms of wage discrimination are covered under Title VII of the Civil Rights Act of 1964.
Step-by-step explanation:
The Equal Pay Act of 1963 is a significant labor law specifically designed to prohibit wage discrimination based on sex. Under this Act, it is illegal to pay different wages to employees of opposite sexes if they perform jobs that require substantially equal skill, effort, and responsibility under similar working conditions. This landmark legislation was established to address the wage gap where female workers on average earned less than male workers. It is one of the statutes in the United States aimed at reducing earnings gaps and ensuring fair employment practices.
While the Equal Pay Act addresses discrimination based on sex, other forms of wage discrimination such as race, color, national origin, and religion are prohibited under Title VII of the Civil Rights Act of 1964. Differences in pay may legally exist when they are based on seniority, merit, quantity or quality of production, or any other factor other than sex. Therefore, the correct answer to the given question is B. Sex.