The 700,000-member Service Employees International Union California endorsed Lt. Gov. Gavin Newsom for governor and state Sen. Kevin de León for U.S. Senate on Tuesday, giving the Democrats a powerful union ally to supply grassroots campaign help.

“SEIU California members are ready to work to see Gavin Newsom sworn in as California’s next governor,” Roxanne Sanchez, president of SEIU California, said in a statement Tuesday. “We believe that California can show the nation the way forward to a society that values every person and makes real progress toward economic and racial justice. Gavin Newsom will be both a visionary leader and, more important, a partner of working people in accomplishing these goals.”

Union officials praised de León as someone who “speaks up for California values.”

“Kevin shouldered our fight for the $15 minimum wage across the finish line, holds a strong record on environmental justice and fought valiantly to protect our immigrant communities when the Trump administration moved to openly attack them and divide families,” said David Huerta, a union board member.“He’s stood up for us and our California values again and again.”

SEIU has long been one of the state’s most politically active unions, spending upward of $300,000, for example, to help elect Wendy Carrillo to the Assembly from Los Angeles in a special election in December.

While union officials said it was too early to predict how much they would spend on the campaigns, most of their expenditures would be in the form of union members doing grassroots campaigning.

“We’ll be focusing on getting people on the ground,” Quintin Maidment, a spokesman for SEIU Local 2015, said Tuesday. Given that most of the union’s membership is based in Los Angeles County, the union will focus its campaigning there, as well as the Bay Area and in communities of color across the state.

It’s one of several big union endorsements announced recently in the gubernatorial race. Earlier this week, former Los Angeles Mayor Antonio Villaraigosa won the support of the California Police Chiefs Association and the Peace Officers Research Association of California, which represents more than 70,000 public safety officers — the largest law enforcement organization in California.

Newsom and Villaraigosa were virtually tied in a survey this month from the nonpartisan Public Policy Institute of California. De León badly trails incumbent U.S. Sen. Dianne Feinstein, D-Calif.

Joe Garofoli is The San Francisco Chronicle’s senior political writer. Email: jgarofoli@sfchronicle.com Twitter: @joegarofoli