Which factor is NOT a ground for discrimination according to employment legislation?

Employment duration is generally not considered a ground for discrimination according to employment legislation. Factors such as age, sexuality, and union membership are explicitly protected against discrimination in most legal frameworks. They are categorized under equal treatment provisions that aim to ensure no individual is treated less favorably due to inherent characteristics or choices that do not affect their ability to perform a job.

Union membership is relevant because legislation protects workers from discrimination based on their involvement in trade unions or collective bargaining activities. Age and sexuality are also protected characteristics, with specific laws in place to prevent inequalities based on these attributes, ensuring that individuals are not sidelined or unfairly treated in workplace settings.

In contrast, employment duration—the length of time an employee has worked with an organization—does not inherently confer a status that warrants protection against discrimination. While length of service can impact certain employment rights or benefits, it does not fall under the categories typically highlighted by anti-discrimination laws. Hence, employment duration is not recognized as a ground for discrimination.