SAN JOSE — Silicon Valley commuters may need to brace themselves for an extra dose of traffic gridlock next week, as transit workers in Santa Clara County prepare to go on strike.

The Amalgamated Transit Union Local 265 will vote Wednesday night on whether to accept the Santa Clara Valley Transportation Authority’s (VTA) “last, best, and final” offer. John Courtney, the union’s recording and financial secretary, said the union would likely announce the outcome of the vote Thursday morning along with any plans to strike, should the workers reject the VTA’s proposal.

The local — which received approval April 9 from the South Bay Labor Council to go on strike — said Monday it was likely the union would not accept the proposed contract.

“All bets are off after Wednesday,” the union said via Twitter.

I can tell you the ATU will vote the Last Best and Final offer down on Wednesday. It will be an overwhelming NO vote! ALL BETS ARE OFF AFTER Wednesday. — ATU265RFS (@ATU265RFS) June 18, 2019

If the union does agree to strike, it would need to provide the VTA at least 72 hours notice before any work stoppage, said VTA spokeswoman Brandi Childress. As soon as the union notifies the VTA of the strike, it will inform the governor’s office, which has 72 hours to issue a ruling preventing the action, should it find the stoppage would create a public safety hazard.

Courtney declined to comment Wednesday on the union’s plans, but Childress said given the timeline, the VTA is anticipating any strike, should it move forward, would happen sometime next week.

If that’s the case, the VTA would stop all light-rail service, Childress said, and bring in licensed bus operators from other transit agencies along with private operators to drive buses on some of the authority’s most trafficked routes. The VTA serves around 118,000 customers each weekday on its light-rail trains and buses, with the bulk of passengers — about 91,000 — riding its buses. The routes extend from Palo Alto to Gilroy in Santa Clara County.

Although the draft contingency plan is still being finalized, Childress said the authority will focus on maintaining service on the Line 22 bus, its busiest route, which runs from Palo Alto to East San Jose and carries about 9,000 people each weekday. If enough replacement bus operators can be found, Childress said, the next priority will be the Line 68 bus, which runs from San Jose’s Diridon Station to the Gilroy Transit Center and carries about 4,500 passengers daily.

“It’s a big impact,” Childress said. “We’re hoping for the best and that the union finds the offer agreeable and equitable.”

The two sides have been negotiating since August on a new contract but reached an impasse on May 10, she said. They’ve signed 26 out of 37 tentative agreements, but there remain disagreements over pay, pensions and scheduling, among other issues.

The VTA is offering an 8 percent wage increase over three years, with 3 percent in the first year and 2.5 percent in the second and third years. Union representatives said the increase does not do enough to cover the actual cost of inflation, which rose by 4 percent in the last year alone, according to the US Department of Labor’s Consumer Price Index.

The VTA is also offering a one-time, lump-sum payment of 3.1 percent of workers’ salaries that would be doled out in increments over the three-year contract. The payment is meant to help offset the pension contributions the VTA is asking ATU members to make, the VTA said.

The increased pension contributions are a sticking point for the authority, Childress said. The ATU is the only bargaining unit at the VTA whose members don’t fully contribute to their pensions.

“Doing so would ensure long-term financial sustainability for the organization,” she said, “while still providing equitable and competitive compensation for it’s employees.”

Union officials have rejected this claim. In a statement posted to Twitter on June 14, the union noted, “Any increase to the pension contribution will be permanent and the lump sum payment will only be for the next three years.”

Union representatives have also taken issue with an increase in the number of “split shifts” that bus and light rail operators are required to work, forcing workers to take time off after a morning shift before having to return to work in the evening. Roughly 31 percent of VTA’s employees live outside the county, according to the authority.

“Many of our members cannot afford to live where we work so we commute long distances to and from work,” the union said via Twitter. “VTA is pushing to increase an all ready [sic] unsafe working condition.”

Facing a $25 million shortfall, the VTA in May approved a new service plan with 63, mostly small, cuts to curtail service, often in the form of reducing weekend routes or eliminating them altogether, shaving off a few hours at the start or end of the day, or running buses less frequently.

A few bus routes were eliminated entirely, as was light-rail service along the Almaden spur, which affected two stations. But the authority also increased service on some of its busiest and most-used routes through downtown and East San Jose.

The 8 percent increase to workers’ base salary, plus the 3.1 percent one-time bonus, would add about $27.7 million to the budget over the three-year contract period, Childress said. Together with other wage and benefit adjustments the VTA is offering, the total cost of the new contract would be nearly $31 million, the VTA said.

The ATU is the VTA’s largest union, Childress said. It represents about 1,600 employees, including roughly 1,100 bus and light rail operators, plus mechanics, dispatchers, some facility workers and customer service representatives. The VTA has about 2,200 employees, including many represented by two other unions, the SEIU and AFSCME, which Childress said are both expected to support ATU in its strike.

Correction: An earlier version of this story incorrectly stated the Line 65 bus route had already been eliminated. The VTA’s Board of Directors voted in May to delay elimination of the route until the end of the year and will reassess in August whether to save the route.