OAKLAND, Calif. -- During a Friday press conference, BART officials accused union leaders of not acting in good faith in contract negotiations that have led to calls to strike.

The leaders of Amalgamated Transit Union Local 1555 had reached a tentative deal with Bay Area Rapid Transit, but members then rejected it. The union represents about 900 train operators, station agents and power workers

At a news conference Friday, Bay Area Rapid Transit spokesman Linton Johnson pointed to a memo by the union president to its members, describing the contract proposal as "ugly" and containing "downsides." Johnson says that shows leadership was not acting in good faith.

At one point during the press conference, Johnson actually suggested that BART passengers to confront train operators and station agents about this strike. He later retracted that statement.

Further negotiations have broken down, and no new talks are currently scheduled.

The union, which represents train operators and station agents, is set to go on strike Sunday evening.

If the ATU follows through on its strike threat it will be the transit agency's first strike since September 1997, when a five-day strike created havoc for commuters.

At a news conference outside the union's office across the street from the Lake Merritt BART station Thursday, ATU Local 1555 President Jesse Hunt said, "We have no choice" but to go on strike after BART board members voted 9-0 earlier in the day to impose pay and work rules on the union, effective immediately.

Hunt cited the fact that the implementation of terms and conditions of employment brought members of the ATU under a contract "far worse than the contract that was in front of our union this week" as the main reason behind the strike.

"It's a regressive proposal that will net a seven percent pay cut to our members as well as eliminate our social security," said Hunt during the strike announcement.

Hunt said BART riders should look to alternate means of getting to work on Monday.

BART averages 340,000 passengers on weekdays. Metropolitan Transportation Commission spokesman Randy Rentschler said that represents about 180,000 riders a day, as many people take roundtrips.

Two other BART unions voted earlier this week to approve management's contract offer but their leaders have said they would respect picket lines if ATU Local 1555 goes on strike.

The other unions are Service Employees International Union Local 1021, which represents about 1,500 mechanics, custodians, safety inspectors and clerical employees, and American Federation of Local, State and Municipal Employees Union Local 3993, which represents about 200 middle managers.

Asked by reporters if a strike could still be averted, Hunt said, "Anything is a possibility now" but at this point no contract talks are scheduled before Monday.

BART spokesman Linton Johnson put the blame for a possible strike squarely on ATU Local 1555, saying, "If they go on strike, it's all on them."

Johnson said the only way he can see to avert a strike is for the union to come back to the negotiating table and help BART, which is facing a $310 million budget shortfall over the next four years, meet its goal of saving $100 million in labor costs over that time period.

Johnson said ATU must do its part to trim labor costs because the other two unions agreed to cost-saving measures and BART passengers have been doing their share by paying higher fares since July 1.

However, Hunt said ATU members, who rejected BART's contract offer by a margin of about two-to-one on Monday, are going on strike because "it's matter of fairness and equity" and they think they are being forced to accept "an unfair burden."

Gov. Arnold Schwarzenegger, who previously said he would not order a cooling-off period in the contract talks, called on "both parties to get back to the negotiating table and reach an agreement before any strikes or other job actions are taken."

In a statement, Schwarzenegger said, "Both sides need to resolve their disputes and come to an agreement before taking drastic action that will have an immediate effect on the daily lives of so many Californians."

He said the State Mediation & Conciliation Service, under the Department of Industrial Relations, is available to facilitate negotiations and help reach an agreement.

BART began contract talks with its unions on April 1. The transit agency's contract with union employees was scheduled to expire on June 30 but was extended to July 9 after four state mediators joined the talks.

Employees kept working without a contract after an agreement wasn't reached by July 9 and a tentative agreement with all three unions was announced on July 31 after a 27-hour all-night bargaining session.

Before the BART board voted Thursday, board member Lynette Sweet of San Francisco said she reluctantly supported imposing terms and conditions of employment on ATU members because, "We can't keep going though deadline after deadline after deadline with no give and take."

Board member Gail Murray of Walnut Creek said "it's not fair" to the other two unions for the talks with ATU Local 1555 to go on and on.

Murray said the other two unions and BART riders "have done their share" to help BART address its financial problems and it's up to ATU Local 1555 to do its share.

Board member Joel Kelley of Antioch said BART has to cut its costs because "all of our economic indicators are going down," as ridership has declined by about 11 percent and sales tax revenues also have decreased significantly.

BART management declared an impasse in its talks with ATU Local 1555 late Wednesday night after the union rejected what management said was its last, best and final contract offer.

But Hunt said he didn't think an impasse had been reached and he thinks talks with management on Wednesday were "fruitful and productive."

Hunt said the union is considering going to court to challenge the legality of BART imposing terms and conditions of employment on the grounds that an impasse wasn't reached and management hasn't bargained in good faith but hasn't taken that step so far.

San Francisco Mayor Gavin Newsom, like Schwarzenegger, also called on ATU Local 1555 and BART to go back to the bargaining table.

In a statement, Newsom said, "Halting service to BART's 340,000 daily riders will hamstring Bay Area commuters, clog our freeways, and affect businesses across the region as workers and consumers are left stranded."

He said, "All jurisdictions are feeling the pain of the tough economic climate and a BART strike that strands riders will only make it harder for everyone who lives and works in the Bay Area and relies on public transportation."

Rentschler said virtually all Bay Area commuters will be affected by a BART strike because such a labor action will have a domino effect on other transit services.

He said, "Caltrain and the San Francisco Municipal Railway will be affected" and traffic in the Caldecott Tunnel will be heavier and slower than normal.

Rentschler said other transit agencies simply don't have the capacity to serve all the BART riders who will have to find other ways to get to work on Monday.