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Tech has big plans for drones. A cadre of startups are building, flying and selling them, and behemoths Amazon and Google have ambitious delivery projects in the works. Now policy groups tied to these tech firms are scrambling to block legislation moving through California that could dash those dreams, seriously impeding efforts to deploy drones for commercial use.

Senate Bill 142 restricts the flight of unmanned aerial vehicles under 350 feet above properties without the permission of those property owners or legal entities. The bill passed the California Assembly on Monday, by a wide margin (56 to 13), and is heading to the state senate for a vote soon. If passed, it would land on the desk of California Governor Jerry Brown.

If signed, advocacy groups that represent many of the largest Silicon Valley firms say it would create a litigious nightmare, hamper public use cases of drones and land a blow to a burgeoning tech market.

The Consumer Electronics Association has estimated that unmanned vehicles will generate $14 billion in economic impact in the state over the next ten years — from recreational sales windfalls to broader use cases, like delivery or emergency response services. That impact could be knocked out by the bill, the association wrote to its sponsor, State Senator Hannah-Beth Jackson.

“This is problematic for this growing industry, and just not the kind of good public policy we need right now,” said Doug Johnson, VP for technology policy at CEA.

“It’s fundamentally a ban on commercial use,” said John Doherty, a VP at TechNet, a lobbying group whose clients include Amazon and Google. GoPro, which announced its recreational drone devices in May, has also been actively involved in opposing the legislation.

For her part, Senator Jackson positioned the bill as a privacy issue. As drones rise in popularity, concerns rise too about unwanted drones floating above us.

“Drones are a new and exciting technology with many potentially beneficial uses,” Senator Jackson said in a statement. “But they should not be able to invade the privacy of our backyards and our private property without our permission.”

In June, the bill’s language was tweaked, moving from requiring the “consent” of property owners for drones to fly to demanding “express permission.” That new language, tech advocates said, refocuses the bill on property rights and tightens restrictions on potential uses.

One particular use — the one that has Amazon and Google pouring dollars into Sacramento — is on commercial delivery. Amazon announced its drone delivery plans (flamboyantly) in 2013; Google unveiled its own, Project Wing, part of Google X, the following year.

Advocates said that the bill’s height restrictions (most drones now operate somewhere between 200 feet and 500 feet above ground) and consent rules would cripple future deliveries. How can you get an Amazon package at your doorstep if your neighbor’s yard is a no-fly zone?

Sources close to the Senator’s office disagreed, noting that these drones were sophisticated enough to drop vertically for the intended customer.

Google declined to comment, pointing to advocacy groups like CEA and TechNet. Amazon did not respond to a request for comment.

Another issue for the advocacy groups is that with the bill, California is treading on federal turf. The FAA is set to issue national regulation on drones next month, something Silicon Valley prefers — at least for now. “It’s way better for us to have a national model for drones,” said Doherty. “This is California trying to assert its jurisdiction in the area.”

California is not alone. According to the National Conference of State Legislatures, 46 different states have weighed 156 different drone bills in 2015 alone.

Michael Drobac, executive director of Small UAV Coalition, an industry advocacy group, noted that these state lawmakers are fighting a losing battle. “They want to make mischief,” he said. “They’ll ultimately fail, because technology always wins.”