Chief Executive Elon Musk barked at engineers on the Fremont, California assembly line. Tesla Inc tapped workers from other departments to keep pumping out the Model 3 electric sedans, disrupting production of the Model S and X lines. And weekend shifts were mandatory.

Tesla pulled out all the stops in the final week of June to meet its goal of making 5,000 Model 3s in a week, according to employees who spoke to Reuters. The sedan is essential to put money-losing Tesla on a path to profitability and prove that the electric car company can master mass production.

Whether Tesla can do it week in and week out - and without relying on overtime and extra hands - is another question, and one that weighed on investors.

Shares closed down 7.2 percent at $310.86 on Tuesday.

Leading up to Sunday morning's production milestone, Musk paced the Model 3 line, snapping at his engineers when the around-the-clock production slowed or stopped due to problems with robots, one worker said.

Tesla built a new line in just two weeks in a huge tent outside the main factory, an unprecedented move in an industry that takes years to plan out its assembly lines, and said the tented production area accounted for 20 percent of the Model 3s produced last week.

“They were borrowing people from our line all day to cover their (Model 3) breaks so the line would continue to move,” said a Model S worker on Sunday.

“They’ve been throwing Model 3s ahead of the S to get painted to try to assure that they make their goal of 5,000,” the worker said. “The paint department can’t handle the volume.”

Because of the focus on the Model 3, the S line was about 800 cars behind schedule to enter the paint shop, the worker said.

Any potential disruption of the Model S and X lines could threaten Tesla’s target of building 100,000 of those vehicles in 2018. Tesla built 49,489 of those cars in the first half of this year.