A long, drawn-out battle over “right to repair” from nearly a decade ago is heating up in Massachusetts as groups clash over a ballot question that would update an existing law and expand access to mechanical data related to vehicle maintenance and repair.

The dispute has once again pitted independent repair shops and aftermarket parts retailers against most major automakers, with both sides spending millions to tilt voters in their favor.

Massachusetts’ right-to-repair law — enacted in 2013 and adopted a year later as a national standard by automakers and independent garages and retailers — mandates vehicle owners and independent repair shops have access to the same diagnostic and repair data that automakers make available to their franchised dealerships and certified repair facilities.

The initiative up for a vote in November would give vehicle owners and independent repair shops access to real-time mechanical data from telematics, systems that collect and wirelessly transmit information such as crash notifications, remote diagnostics and navigation from the vehicle to a remote server.

It’s also stirring up the debate over consumer privacy, data ownership and usage rights.

“We know this data is incredibly valuable, and it’s important for a lot of different players in the ecosystem,” said Chelsey Colbert, policy counsel for mobility and location data at the Future of Privacy Forum, a Washington-based think tank jointly supported by foundations and corporate sponsors, including some automakers and tech companies.

But who owns and gets access to the data generated and collected by a vehicle and decides how it is used remains an open question.

Supporters say the initiative closes a loophole in the current law that exempts data transmitted wirelessly through telematics systems while giving vehicle owners more choice and control over their data.

“Building silos for data within the manufacturer is really not a sustainable solution,” said Aaron Lowe, senior vice president of regulatory and government affairs at the Auto Care Association. “The car company is responsible for building cybersecurity protections for the vehicle, but they can provide a gateway where that data can be shared in a standardized way with entities outside of the vehicle manufacturer,” he said.

Lowe referred to automakers today as “the entire gatekeeper for the vehicle” and said they’re making it more difficult to get access to on-board diagnostics, especially in newer vehicles, which is a concern for independent shops.

“We hope that the Massachusetts ballot initiative will be the beginning of a movement to ensure that vehicle owners have the ability to send their mechanical data to the shop of their choice, ensuring a competitive repair industry for consumers nationwide,” he said of the measure’s potential national implications.

Tommy Hickey, director of the Massachusetts Right to Repair Committee, of which the Auto Care Association and O’Reilly Auto Parts are top donors, said it’s about maintaining “a level playing field.”

Critics, however, say the measure is a “data grab” by independent repair shops and big-box aftermarket parts stores and poses cybersecurity, personal safety and privacy risks to vehicle owners.

“A less-expansive version of the Massachusetts proposal failed in California because of concerns around privacy, safety and domestic violence. Those same issues — and many more — are at play in Massachusetts,” John Bozzella, CEO of the Alliance for Automotive Innovation, said in a statement to Automotive News. He deferred further comment to the Coalition for Safe and Secure Data, a group funded by the alliance and many major U.S. automakers.

The coalition’s opposition strategy has included a series of TV ads claiming a stalker or sexual predator could gain access to personal data in a vehicle and use it to target their victims. Some media outlets have called the ads misleading, fearmongering and out of context. But Conor Yunits, chief spokesperson for the Coalition for Safe and Secure Data, said the claims are justified.

“Those are rationales laid out by domestic violence prevention advocates, both in Massachusetts and in California,” he said. “They’re very real risks.”

Massachusetts State Automobile Dealers Association Executive Vice President Robert O’Koniewski argues independent repair shops already have access to everything they need to diagnose and repair a vehicle, and consumers can choose where to get their vehicles fixed.

“We feel that a lot of the proposal is completely unnecessary, that the right-to-repair law that is on the books today works just fine,” he said, adding that the association is “adamantly opposed” to the initiative.

“It’s not as if there’s a monopoly by [franchised] dealerships,” O’Koniewski said. “The large bulk of post-warranty work is being done by independents.”