Union leaders weren't immediately available for comment.
The contract for employees represented by Amalgamated Transit Union Local 192 expired at midnight Sunday but union leaders have agreed to temporarily extend the contract while negotiations continue.
Bus agency spokesman Clarence Johnson said in a statement, "The ongoing negotiations are a signal that operators will be on the job Wednesday providing bus service as usual."
Johnson said, "Reportedly, there has been some slight progress in the negotiations over the past few days as both sides have altered their stances, if but modestly."
He said, "AC Transit management, in an effort to avoid a service disruption and keep negotiations on track, is proposing pay increases to the ATU employees along with some modification to current work rules and practices that will aid the district in efficiency and sustainability."
Earlier today, ATU Local 192 said in a statement, "We are at the table and bargaining, but our members will not support going backwards."
The union said management negotiators "need to bargain a fair contract that moves things forward, not backward."
ATU Local 192 represents 1,760 bus drivers, mechanics, dispatchers, clerical and other workers.
The bus agency serves parts of Alameda and Contra Costa counties.
The union has said it will give 24 hours' notice before going on strike.