With the threat of a strike looming again, the BART board will hold an emergency meeting within a day or two to discuss whether to carry out its threat to impose pay and work rules on a union that rejected a tentative four-year contract settlement.

The mixed results Monday of contract ratification votes by two unions — one approving and one rejecting — threw a wrench in BART's hopes to be done with a rancorous labor negotiations that have more ups and downs than a bumpy airplane ride.

The union for station agents and train operators — Amalgamated Transit Union Local 1555 — announced late Monday night that its members rejected the four-year contract settlement by a margin of 64 percent opposed and 36 percent in favor. Earlier in the day, the largest BART union representing mechanics, clerks, janitors and track workers — Service Employees Union Local 1021 — announced that 70 percent of its voting members ratified the contract.

BART managers and union officials said it's unclear what will happen next, but they agree the risk of a strike has been ratchet up.

BART Board President Tom Blalock said the board plans to hold an emergency session later this week to discuss whether to unilaterally impose pay and work rule terms on the train operators and station agents, a move would further up the stakes in the standoff with that union.

"We regret that BART employees represented by the Amalgamated Transit Union have voted to reject a labor agreement that was approved by 75 percent of BART's largest union, SEIU," Blalock said in a written statement early this morning. "The BART board will now schedule a special meeting to consider its options, including implementing terms and conditions of employment until a new labor agreement can be reached."

Under state law, a local government board must give the public 24 hours notice before holding an emergency meeting.

Jesse Hunt, president of ATU Local 1555, said his union is asking BART to reopen labor negotiations to try to come up with a two-year agreement, rather than the four-year deal that his union rejected Monday.

"The ball is in their court," Hunt said. He added that his union would be read to resume talks as early as Wednesday.

Hunt said some of his union members were unhappy that the tentative agreement locked them into a wage freeze for four years even if the economy turns around before the contract is up. While the contract deal would provide bonuses in three of the four years, it would not boost the base pay, he noted.

BART spokesman Linton Johnson expressed frustration that the train operators and station agents voted down a deal after four months of difficult negotiations that included two extensions of talks and a 27-hour marathon bargaining session that produced the tentative accord. "We're at our wit's end," he said this morning.

He said BART has said since contract talks started April 1 that the transit system needs $100 million in labor savings over four years through changes in benefit costs and work rules.