California Democratic Party Chairman John Burton says one of the state's most politically powerful unions has threatened to cut off funding for the party over his support for a group that has broken away from the labor organization.

The rift could drive a wedge between the party and one of its most generous donors. The state council of the Service Employees International Union has directed $700,000 to the Democratic Party since 2007 and millions more to Democratic candidates and causes.

Burton said SEIU’s California president, Bill Lloyd, made the threat as Burton was set to appear last week at a San Francisco fundraiser for the splinter group, the National Union of Healthcare Workers.

"They threatened me," said the 76-year-old Burton.

Burton said that he was championing union workers "when [SEIU's national president] Andy Stern was in college." He hailed the breakaway union's leader, Sal Rosselli, as a lifelong friend and “one of the strongest labor leaders in this state.”

Mary Gutierrez, a spokeswoman for SEIU’s state council, would neither confirm nor deny any warning from Lloyd to Burton. “Formal discussions haven’t been had with our board," which would have to vote to cut off funding, she said.

-- Shane Goldmacher in Sacramento