Bay Area Rapid Transit workers said they'll strike -- affecting 400,000 San Francisco-area commuters -- if there is no contract agreement by midnight Sunday.
BART and workers associated with transportation unions ended a four-day strike over pay and benefits in July, agreeing to a 30-day extension in negotiations.
That period is up Sunday at midnight and union workers warned they will go on strike again if a new agreement is not reached by then, CNN reported.
"It is unfortunate that we find ourselves in the same situation that we were in 30 days ago, with no real progress made by management to address worker concerns about safety and wage cuts," union President Roxanne Sanchez said in a statement.
Workers had initially asked for a 21 percent pay raise and BART proposed 2 percent pay increases over four years.
Pete Castelli, executive director of Service Employees International Union Local 1021, said BART's proposed increase in pay would be wiped out by its plan to increase how much employees pay toward their benefits, making them worse off.
In the past 12 years, BART's health insurance costs have shot up by 251 percent, with workers' payments increasing from $25 per month to $92 per month, the San Francisco Chronicle reported. Pension costs have increased by 126 percent since 2005 and workers pay nothing toward the benefit.
"This next contract must address the skyrocketing cost of employee benefits," said Jim Allison, a BART spokesman. "Health costs are rising and we have to have employees share in some of that risk."
BART said union train operators and station agents average about $82,000 per year, including more than $10,000 in overtime pay.
About 400,000 people use BART transportation daily.