Musk describes the contractor situation within Tesla as being like a "Russian nesting doll" and that some perform "worse than a drunken sloth".
Tesla did not immediately respond to a request for comment.
The company's shares rose as much as 2.7 per cent in after-hours trading.
Tesla needs to make 6,000 Models 3 units per week by the end of June.
"We will be stopping for three to five days to do a comprehensive set of upgrades".
A total of 34,494 vehicles were produced during the first quarter of 2018 taking all Tesla models into account - including 9,766 Model 3s alone, with the automaker delivering 8,180 Model 3 sedans, 11,730 Model S sedans and 10,070 Model X crossovers during this period. The stock price has dropped about 8 percent since January as many investors grow increasingly skeptical that CEO Elon Musk will be able to back up his bold promises for the electric vehicle company.
With everything riding on the Model 3's success and delays to customers with money down, any other billionaire would have people spitting bricks at him.
Canelo Alvarez receives drugs ban, new Gennady Golovkin rematch date planned
Now that Alvarez is suspended, Golovkin will now face Vanes Martirosyan on May 5 from the StubHub Center in Carson, California . Normally boxers are hit with a one-year ban for using PEDs, but first-time offenders usually get six months.
The automatic blog Jalopnik had first published Elon Musk's email on Tuesday and the authencity was confirmed by sources. The extra workers will help the company add a third shift of work for the "assembly, body and paint", allowing the facilities 24/7 operations.
Musk's email doesn't elaborate on the specifics of how a third will be added to the production schedule.
Elon Musk recently used Twitter to admit "excessive automation" at Tesla factories were harming productivity, and contributing to the brand's widely-reported "production hell". The company had previously said it was targeting 5,000 a week by around the end of the second quarter. Musk touched on why he was setting a higher target internally than the one the company has communicated publicly in his email.
TSLA had said previously that it was targeting 5K Model 3 cars per a week by the end of Q2, but "we can not have a number with no margin for error", Musk said. "We will keep going until the Model 3 build precision is a factor of ten better than any other auto in the world", he added.
"Thanks for being such a kickass team and accomplishing miracles every day".
"We are burning the midnight oil to burn the midnight oil", he said.