Which of the following characteristics was the most recent to be protected against employment-related discrimination under federal law?

The most recent characteristic to be protected against employment-related discrimination under federal law is gender identity. Gender identity protections have been clarified and enforced through various court decisions and interpretations of existing laws, such as Title VII of the Civil Rights Act of 1964, which prohibits employment discrimination based on sex. This interpretation has evolved, especially in recent years, leading to broader protections that include gender identity and sexual orientation.

Race, disability status, and age have been protected under federal law for a longer period. For example, the Civil Rights Act of 1964 established protections against race discrimination, the Americans with Disabilities Act (ADA) was enacted in 1990 to protect individuals with disabilities, and the Age Discrimination in Employment Act (ADEA) has been in place since 1967 to protect workers aged 40 and older. Therefore, gender identity is the characteristic that marks the most recent expansion in the scope of protections against employment-related discrimination under federal law.