Lawrence Livermore National Laboratory plans to cut about 500 jobs.
It's one of nation's premier nuclear weapons labs.
Management's blaming the job cuts on rising costs and potential federal budget cuts.
The layoffs will mostly affect support and operations employees.
Officials say the laboratory's goal is to protect scientific research positions, but added that it's not currently known whether any scientists will be laid off.
The lab is part of the Energy Department's National Nuclear Security Administration.
It has about 8,000 employees.