California Gov. Jerry Brown, at the request of Bay Area Rapid Transit management, appointed a three-member board of inquiry to look into the stalled negotiations, the San Francisco Chronicle reported Monday.
Transit workers had been scheduled to walk off their jobs at 12:01 a.m. Monday.
In a letter to BART's general manager and three top union leaders, Brown said he was intervening because a strike "will significantly disrupt public transportation services and will endanger the public's health, safety and welfare."
Under Brown's terms, the board must give the governor a written, public report on contract talks within seven days, during which time unions cannot walk off the job and BART cannot lock them out. After receiving the report, Brown must then decide whether to enforce a 60-day cooling-off period, which would delay any possible strike until mid-October at the earliest, the Chronicle said.
Union officials earlier Sunday had rejected BART's proposal for delaying the strike for a week so talks could proceed.
A management spokesman denied that BART was trying to break its unions.
The sticking points are pay raises, healthcare and pensions, the Chronicle said.
BART's two largest unions -- the Amalgamated Transit Union and Service Employees International Union Local 1021 -- gave notice Thursday that their 2,600 workers would strike Monday if no agreement was reached on a contract by midnight Sunday.
Union workers walked off the job during a 4 1/2-day strike in July. State negotiators suggested the 30-day contract extension that lasted until Sunday.