SACRAMENTO (CBS/AP) — California corrections officials say that nearly 40 percent of the state’s inmate firefighters have previous convictions for violent offenses.

In a sharp reversal from the agency’s claim for years that only nonviolent inmates were allowed in the program, corrections spokesman Jeffrey Callison says they have been serving since at least the 1990s.

READ MORE: Police Investigation of Shattered Vehicle Windows Temporarily Shuts Highway 17 Saturday

Callison says the department gave The Associated Press and others inaccurate information. He blamed the misstatement on differing definitions of what constitutes a violent background.

READ MORE: Storm Watch: Evacuation Orders Issued for CZU Burn Zones in Santa Cruz County

The disclosure Wednesday shocked officials with the state’s firefighting agency and the union that represents professional firefighters who oversee inmates on the fire lines.

Firefighters union president Mike Lopez called for a full investigation. He says he’s very concerned that firefighters did not know they were working alongside inmates with a history of violence.

MORE NEWS: Elon Musk, Tesla Super Fans Blast Biden Administration Move Toward Regulating Autopilot

Copyright 2015 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.