nonforfeitable
adjective
non·for·feit·able ˌnän-ˈfȯr-fə-tə-bəl 
: not able to be forfeited : not subject to forfeiture
nonforfeitable rights/contributions
Example Sentences
Recent Examples on the Web Sandi Jacobs of EducationCounsel, a consulting firm, cited eight states that recently doubled — to 10 years — the time a teacher must work before vesting, or earning a nonforfeitable right to a pension. 
Mary Williams Walsh, New York Times, 8 Mar. 2017
Mary Williams Walsh, New York Times, 8 Mar. 2017 Word History
First Known Use
1860, in the meaning defined above