Shuttle bus drivers for five prominent tech companies will decide whether to unionize on Friday in a vote that has the potential to dramatically expand organized labor’s territory in Silicon Valley and embolden others in the tech industry’s burgeoning class of service workers to demand better working conditions.

Drivers who ferry Yahoo, Apple, Genentech, eBay and Zynga workers — all employed by contractor Compass Transportation — will decide whether to join the Teamsters union in an election overseen by the National Labor Relations Board. Union leaders say they want to bring the drivers into the fold so they can negotiate better pay and benefits — as well as relief from a split shift that has the drivers working morning and evening shifts with no pay in between. A contract the Teamsters struck over the weekend for Facebook’s shuttle bus drivers, who work for Loop Transportation, offers a glimpse of what may be possible: paid sick and vacation time, full health care coverage and wages of up to $27.50 an hour.

Hoping the Teamsters can negotiate something similar for Compass drivers, Tracy Kelley, a shuttle bus driver for Yahoo, said he is eager to cast his ballot.

“If I could vote yes a thousand times, I would,” said Kelley, a 51-year-old San Francisco resident.

Kelley said he and his fellow drivers make $18 an hour, which leaves them struggling to get by in the pricy Bay Area. Because they are employed by transportation companies that strike contracts with the tech firms, Silicon Valley shuttle bus drivers’ ties to the likes of Apple are indirect. But advocates cite the firm’s record-breaking profitability to bolster their case that the drivers should be making a better wage.

“This is like chump change to them,” said Rome Aloise, international vice president and secretary-treasurer of Teamsters Local 853. “You’ve got the well-paid being hauled around by people who can’t afford to support their families.” A spokesman for Compass did not respond to a request for comment. Representatives for Apple, Yahoo and eBay did not respond, and a spokeswoman for Zynga declined to comment. A spokeswoman for Genentech stressed that the issue is between Compass and its employees, adding that the tech company will respect whatever decision the drivers make.

Friday’s vote covers about 120 employees, with drivers for Amtrak joining the tech drivers.

Facebook’s shuttle bus drivers voted to join the Teamsters in November and approved a contract on Saturday, setting the stage for Friday’s vote. Although a patchwork of transportation companies serve the valley, the Teamsters will have reached the lion’s share of the shuttle bus drivers if they prevail on Friday, Aloise said.

Amid intensifying scrutiny over the treatment of low-wage workers who keep high-tech campuses humming, organized labor has ramped up its efforts in Silicon Valley. In addition to the campaign for shuttle bus drivers, United Service Workers West is working to organize security guards in the region. During a speech Tuesday at a conference for women in Silicon Valley, former Secretary of State Hillary Clinton cited the security guards’ campaign as an example of a “movement stirring across our nation.”

The Teamsters’ growing footprint may well trigger more organizing among service workers in the high-tech industry, said Alan Hyde, a professor at Rutgers School of Law-Newark. Rewarded with high salaries and lavish perks, tech workers have shown little appetite for unionization. That, coupled with the valley’s libertarian bent, has created a culture in which it has been harder for service workers to band together, Hyde said.

One notable exception was the Justice for Janitors campaign, which swept the valley in the 1990s, starting with Apple. At least 80 percent of janitors in the valley now belong to United Service Workers West, a spokesman said. But organized labor notched few wins in the intervening years.

A growing nationwide conversation about the income gap seems to have set the stage for union campaigns in the region, Hyde said. Highly skilled workers in Silicon Valley have a median income of $118,700, compared with the $27,000 for workers in low-skill jobs, according to a recent report from Joint Venture Silicon Valley.

“Now is the opportunity for shuttle bus drivers, for food service workers, for janitors, for security officers to re-ask the question: Should I be equally as valued as the high tech workers in the high tech industry?” said David Huerta, president of United Service Workers West.

The contract approved by the Facebook drivers calls for guaranteed overtime after an eight-hour workday, up to five weeks of paid vacation and contributions to retirement plans, among other benefits. Depending on the vehicle they operate, drivers can make up to $25 per hour, with wages set to rise over the years. The drivers made less than $18 per hour on average before, Aloise said.

If drivers opt to work the split shift, they will make more per hour — up to $27.50 — to compensate them for the downtime.

Aloise said the Teamsters plan to negotiate the same terms across the valley.

“Our goal is to have a master agreement including these wages, benefits and working conditions for all of the contractors in the tech industry,” he said.

That would be welcome relief for Kelley, who all but lives in a double-decker bus.

The first leg of the Yahoo shuttle bus driver’s workday starts at 6 a.m., when he ferries high-tech workers from their pads in San Francisco to their desks in Sunnyvale. He is stuck in the South Bay from 9:30 a.m. until they begin trickling out of offices for the ride home around 4:30 p.m., unable to return to his own residence in San Francisco — and earning nothing during the seven hours of downtime. His bus is his livelihood, his home office and the place where he steals a few hours of sleep midday.

“The split kills me,” he said.

Kelley began driving for Compass about a year ago, having been laid off from his post as a vice president of Union Bank.

Contact Julia Love at 408-920-5536, or follow her at Twitter.com/byjulialove.