Two of the biggest police surveillance companies in the U.S. are ending a long-standing partnership, in what’s become a bitter, public spat with each claiming the other is at fault.

Earlier this week, Rick Smith, the billionaire CEO and cofounder of $50 billion market cap police tech giant Axon Enterprise, emailed a letter to customers saying it was cutting ties with Flock Safety, a $4.5 billion-valued provider of AI-powered license plate reader tech, used across more than 40 states in the U.S. “Flock has demonstrated a pattern of behavior that creates barriers for customer integrations in attempts to create a digital silo and coerce customers to purchase additional Flock services over Axon’s,” Smith wrote in the email, which was obtained by Forbes.

The note was in response to a blog post from Flock CEO and cofounder Garrett Langley, who claimed Axon’s decision to end the partnership was a “surprise decision.” But Smith was clear on his reasons.

“Axon decided that being open and collaborative is ‘no longer in Axon’s best interests,’ and no additional reason was given to us.”

Garrett Langley, Flock Safety CEO

He accused Flock of charging excessive fees for integrating with Axon’s technologies, in particular Fusus, software that combines surveillance feeds into one app and uses AI to alert cops if criminal activity is spotted. Smith claimed that Flock had recently “escalated” tensions between the two companies by refusing to allow any Flock feeds to go through to Fusus’ software, “in an effort to strong-arm customers to switch to its platform.”

Smith signed off by saying that he felt “embarassed” that he’d recommended Flock to customers, apologizing “that the situation has deteriorated to this point.” He included Langley’s email address, in case customers wanted to speak with the Flock founder directly.

Cops are already fretting about what the bust-up could mean for police. Luis Figueiredo, a police drone pilot in New Jersey, told Forbes that when companies like Axon and Flock don’t work together, it ends up costing cops more.

“They do this so that agencies are forced to go with their ecosystem and not be able to shop around for a better deal or solution,” he told Forbes.

Flock Safety’s senior vice president of policy and communications Josh Thomas said the company wanted to partner with other police contractors, denying Smith’s “baseless accusations about Flock and our team.”

“In fact, a contractual agreement with Axon was recently reciprocated in August of last year confirming that Axon and mutual customers would have free access to Flock’s APIs, until Axon ended that contract a couple of weeks ago,” Thomas added.

In his article on Flock’s website over the weekend, Langley blamed Axon for the bust-up. “Axon decided that being open and collaborative is ‘no longer in Axon’s best interests,’ and no additional reason was given to us,” Langley wrote. He said that attempts to contact Axon executives for a more thorough explanation had not received a response.

He confirmed that Axon will no longer support new “mutual” customers from July onwards. Smith didn’t address that in his message, but did say his company would do what it could to honor existing contracts for combined Axon and Flock tech. Langley said it would continue to send Flock data to Axon users.

It’s a significant altercation, given the two companies’ recent history. Axon was an early investor in Flock, which has raised $680 million to date from VCs including Andreessen Horowitz and Bedrock. Flock has seen enormous success, scoring contracts in as many as 5,000 cities across America, from San Diego to Atlanta. Forbes reported last year on Flock’s aggressive sales strategies, which led to cameras being rolled out in contravention of various states’ Department of Transportation rules on acquiring the right safety permits.

As Flock grew, the two companies expanded their partnership to ensure that Axon users could access Flock’s camera feeds with ease. For cops, that meant more surveillance data in one place.

But more recently their early partnership has been evolving into rivalry. While Flock is the much younger of the two companies, its rapid rise and grand ambition to end all crime with technology, has put it in direct competition with Axon, which originally made its name selling Taser non-lethal weapons, but is now a $50 billion-valued provider of bodycams, digital evidence storage and a plethora of other police tech.

For one, they’ve started competing head-to-head on drones. Last year, Flock acquired Aerodome, a little-known 17-month old startup, for $300 million, while Axon has chosen to promote devices from Skydio, a Silicon Valley-based provider founded by ex-Google engineers.

Others in the market are already trying to capitalize on the fracas. A recently-retired county sheriff chief turned Motorola safety exec shared Langley’s post on LinkedIn, attaching the note, “For those of you that will be negatively impacted by this news, feel free to reach out for a Motorola solution.”

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