Tesla auto workers who are worried about their safety on the job are speaking out.

A new report by the advocacy group Worksafe claims that Tesla's rapid growth comes at the expense of assembly line workers at its factory in Fremont, California, near San Francisco.

The group has released Tesla safety data to back up its claim.

The company says safety is a top priority and always has been, but until now, Tesla has repeatedly declined to release safety records from years past to news organizations.

This new independent report is doing exactly that, reports CBS News correspondent Carter Evans. Evans spoke with the concerned workers and visited the company's California factory.

Tesla factory in Fremont, California. CBS News

"The vehicle itself, is an amazing, you know, accomplishment," said Tesla employee, Michael Sanchez.

Evans asked, "It's how they get it built?"

"And what we have to go through to make that happen for them," Sanchez said.

Four Tesla auto workers say the assembly line at what's supposed to be the "factory of the future" is behind the times when it comes to safety.

"Injuries are the number one problem there," Sanchez said.

"Everybody in our area is burned out. We're trying to run as hard as we can," said Tesla body repair technician, John Galescu.

Galescu wants workers at Tesla to unionize. On the advice of the United Auto Workers union, he legally obtained three years of internal injury reports from the company. An independent analysis of those numbers found that in 2015, Tesla's injury rate was 31 percent higher than the industry average while the rate of serious injuries, ones that resulted in days away from work or restricted duty, was double.

"I don't think it's reflective of where we are currently," said Josh Hedges, Tesla human resources director.

Hedges says safety improvements have already been made. He points to injury numbers from the first quarter of this year, which Tesla says are now 32 percent below the industry average.

"It's coming from a small number that's not really reflective of the environment that you see here," Hedges said of the complaints and allegations.

To prove it, Tesla provided three managers who explained how the company brought in ergonomics experts and added an extra shift.

"Putting in place the three shifts instead of having two shifts of just 12-hour shifts made a huge difference in people's work-life balance. They're not straining their bodies every day all day," said production supervisor, Crystal Spates.

Tesla factory in Fremont, California. CBS News

But these workers say that may not be enough, with what's coming down the line.

The Model 3 is being billed as an affordable electric car for the masses, but making it means a massive production increase for Tesla workers.

"You guys helped produce about 84,000 cars last year. This company is going to be expected to produce half a million of them next year. How are you going to do this?" Evans asked.

"That's a good question," Sanchez said.

"They are under tremendous pressure to build when that happens, you kind of ignore other important issues," said Jose Moran, another Tesla auto worker.



When asked to address the worker's concerns about the expected increase in production, Hedges said, "Tesla is about the safety of our employees. We've built the line with ergonomics involved. So, by no means do production numbers come before the safety of our employees."

Tesla is not disputing the injury rates reported in the analysis.

It's hoping the revamped production line for the Model 3 will reduce injuries even further.

Tesla says its goal is zero injuries.