California police are using decoy “bait buses” to try to catch attackers who have been firing BB guns at coaches taking Google, Apple and other tech company workers from their San Francisco homes to their Silicon Valley offices.

The motive for the attacks is unclear, but previously the luxury coaches – known by the catch-all term ‘Google buses’ - have been the target of peaceful protests by those who blame the influx of thousands of tech workers on gentrification and unaffordable rents in San Francisco.

In the past 45 days there have been at least 20 attacks on the coaches by someone firing metal balls from a BB gun, causing damage to the vehicles’ windows and exteriors.

On January 16 alone, five buses were hit as they carried Apple and Google employees along the Interstate 280 highway between the city and San Francisco Bay area’s Silicon Valley.

In response, Google and Apple changed the routes of their shuttle buses.

The attacks, however, appear to have continued, and after calling in the FBI to assist, California Highway Patrol (CHP) officers have started using the “bait bus” to try to lure in the attacker or attackers.

Revealing the tactic to ABC7 News, CHP Golden Gate Division Commander Ernest Sanchez warned whoever was carrying out the attacks that they would be caught.

“The message is clear,” he said. “If you're shooter out there, it's just a matter of time. We will catch you and prosecute you to the full extent of the law."

It has also been reported that undercover highway patrol officers will board real Google and Apple buses, posing as tech workers and ready to “take appropriate action” if the vehicle comes under attack.

Mr Sanchez said investigators had a description of a vehicle suspected of having been used by the attackers, and, he added, the FBI were examining one of the damaged buses.

"They're looking at damage on the bus and looking at what angle the projectile is coming from," he said.

The charter bus company Storer has also offered a $10,000 reward for information leading to the arrest and prosecution of the attackers.

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As yet the attackers’ motives are unknown, and it is not clear whether the BB shootings are driven by mindless vandalism or are somehow related to a dislike of tech companies.

In the past the shuttle buses that carry thousands of tech workers from San Francisco to Silicon Valley every day have been the subject of non-violent protests by people who fear that the influx of wealthy employees of Google, Apple, Yahoo and others is having a damaging effect on the city.

Between December 2013 to April 2014 the ‘Heart of the City’ group staged peaceful blockades, claiming that the presence in the city of so many high-earning tech workers was leading to gentrification, steep rent rises and the eviction of San Francisco’s previous inhabitants.

There were also complaints that the buses were a symbol of “technological privilege” – free to the tech workers, but effectively using the city’s infrastructure without paying for it.

In February 2013 one non-violent supporter of the protests, the writer Rebecca Solnit, complained: “Sometimes the Google Bus just seems like one face of Janus-headed capitalism.

“The buses roll up to San Francisco’s bus stops, but they are unmarked, or nearly so, and not for the public … The luxury coach passengers ride for free and many take out their laptops and begin their work day on board; there is of course wifi.

“Most of them are gleaming white, with dark-tinted windows, like limousines, and some days I think of them as the spaceships on which our alien overlords have landed to rule over us.”

“All this,” Ms Solnit added, “Is changing the character of what was once a great city of refuge for dissidents, queers, pacifists and experimentalists … Boomtowns also drive out people who perform essential services the teachers, firefighters, mechanics and carpenters.”

“A Latino who has been an important cultural figure for forty years is being evicted while his wife undergoes chemotherapy,” she wrote. “One of San Francisco’s most distinguished poets is being evicted after 35 years in his apartment: whether he will claw his way onto a much humbler perch or be exiled to another town remains to be seen, as does the fate of a city that poets can’t afford.”

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In February 2014, Google donated $6.8 million to the San Francisco Municipal Transportation Agency (SFMTA) to provide free public transit for the city’s low-income children.

In 2015 the SFMTA started a commuter shuttle programme, regulating the routes and sizes of the Google buses, and charging a fee for every public bus stop they used.

Some tech workers also defended their role in the city and denied they were responsible for the high rents and evictions.

One tech worker responded to Ms Solnit by writing as “a member of the invasive species [she] has repeatedly singled out.”

“Anyone who has visited San Francisco,” he wrote in 2014, “Knows that outside a few neighbourhoods the city is about three storeys tall. Paris is seven storeys high almost across the board.

“San Francisco could double in height without greatly hurting its open space or aesthetics. The scarcity of shelter in San Francisco is artificially imposed, the result of a decades-long resistance …

“A recent high-rise on the waterfront was voted down by a coalition of local wealth and the political left, which is also leading the fight against evictions.

“San Francisco’s incumbent residents would prefer the postcard life of a low, sparsely populated city to the high-rises of an Asian megalopolis. Fine. But that means homeowners are forcing the burden of adjustment onto tenants. You can fight development or you can fight evictions, but you cannot logically fight both.”

Saying he hoped San Francisco could be both a “queer refuge” and a home for tech workers, he added: “To read her [Ms Solnit], one would think that San Francisco’s brave natives face a horde of villainous drones and gold diggers.

“But if she made the morning commute, she’d see a lot of Indian and Chinese and Eastern European faces there. In San Francisco’s start-up hostels, you hear half a dozen languages spoken every day.

“Solnit compared tech workers to insects, aliens, Prussian invaders. Applied to any other group, these attempts to dehumanise would have invited howls of indignation.