SAN FRANCISCO (AP) — One out of three grocery workers in California is receiving some type of public assistance while one in five rations the food he or she helps sell, according to a new report that laments the industry’s diminishing standing as a source of stable, middle-class jobs.

For a study set to be published Monday, University of California researchers interviewed 925 people who work for supermarket chains, smaller ethnic markets or in the grocery sections of big box retailers such as Wal-Mart and Target, making it one of the largest surveys ever done of the state’s grocery industry workforce of 383,900, The San Francisco Chronicle reports.

The study was commissioned by a labor union, the United Food and Commercial Workers Western States Council. It found that the median wage at unionized stores fell from $19.38 in 2000 to $15.17 an hour in 2012, with workers at non-union shops earning less than $10 an hour.

“Workers who sell food in California are almost twice as likely as the general population to not be able to afford to eat the food they sell,” states the report by UC Berkeley’s Food Labor Research Center and UC Davis community and regional development professor Chris Benner.

The report’s authors criticized the Safeway and Albertsons chains in particular for using profits to enrich investors instead of reward employees and praised Costco for paying its workers comparatively well, the Chronicle reports.

A private equity firm that already owns Albertsons, Cerberus Capital Management, is in the process of buying Safeway for $9.4 billion. The deal should benefit both workers and customers, Safeway spokeswoman Teena Massingill said.