The AC Transit board on Tuesday requested that California Gov. Jerry Brown intervene in the labor dispute and impose a 60-day cooling off period. The board said that a bus strike would significantly endanger the public's health, safety and welfare.

That request came a day after AC Transit union employees issued a 72-hour strike notice, and comes in the midst of ongoing BART negotiations where two unions from the nation's fifth-largest rail system also may strike. If both agencies strike, the commute could be crippling for Bay Area motorists.

Leaders of Amalgamated Transit Union Local 192, which represents about 1,800 bus drivers, mechanics, dispatchers, clerical and other workers, have said they will strike as of 12:01 a.m. Thursday if a new contract deal is not reached, AC Transit spokesman Clarence Johnson said.

The announcement follows a vote on Oct. 2 in which AC Transit employees rejected by a margin of 561 to 369 management's offer of a 9.5 percent pay increase over three years.

The employees' vote rejecting the contract marked the second time they voted down a tentative agreement. On Aug. 17, members voted by a margin of 576 to 257 against a tentative agreement that had been reached earlier that month.