Looking for a Word

I think "service" might be the word you're looking for.

Look at meaning #1.5 for "service" as a noun in the link below.

http://www.oxforddictionaries.com/definition/english/service

Thank you very much, Teechr. Is that the same word that employers use when they want to hire someone?

It's more likely to be used by a job seeker in a cover letter and/or on their CV.
Do you have a particular sentence/context in mind?

I am working on a table that lists the staff members of a company and groups them based on their "service years". I don't know what word should be used for the title of groups column. Thank you for your help. The text is about management and organizational studies.

Use "Years' service" for your column heading.

Thank you very much, Teechr.

You're welcome.
Note the position of the apostrophe.