• SpaceX, Tesla and Boring Company execs are authorized to work for Elon Musk at Twitter, the social media company he acquired in October, according to internal records.
• SpaceX CFO Bret Johnsen, Tesla CIO Nagesh Saldi and The Boring Company's operations leader Jehn Balajadia are among the execs Musk enlisted to help at Twitter.

Elon Musk led a $44 billion acquisition of Twitter and appointed himself CEO there in late October. Ever since, he has enlisted high-ranking executives and engineers from his other businesses, including SpaceX, Tesla and The Boring Company, to help out at the social media company, according to internal records obtained by CNBC and conversations with recent Twitter employees.

Musk has also enabled partners from investment firms who participated in the Twitter buyout access to work within the social media company.

It wasn't immediately clear how many hours each person had worked so far at Twitter, or how much of their work may be done remotely versus in Twitter's San Francisco headquarters or other offices.

Shareholders remain concerned about how Musk's financial commitments, split schedule and controversial decisions at Twitter may impact the automaker. Tesla shares have declined about 25% since he took over Twitter on Oct. 27.

Internal records obtained by CNBC indicated that more than 50 Tesla employees, mostly Autopilot software engineers, were authorized to work for Musk at Twitter immediately after he took over, and were still authorized to work there as of early December. Included among the names are people previously reported by CNBC, as well as:

• Director of Software Engineering Silvio Brugada
• Director of Infrastructure Engineering and Info Security Rajasekar Jegannathan
• Senior Manager of DevOps Michael Outland
• Director of Battery Manufacturing Engineering Andrew Ross
• Chief Information Officer Nagesh Saldi
• Autopilot Project Manager RJ Sekator

Attorneys asked Elon Musk in a Delaware court in November about his use of Tesla talent at Twitter. The lawsuit and trial is to determine whether Tesla's board followed the law when it granted Musk a massive CEO pay package back in 2018.

The attorneys asked, "Did anyone suggest to you that perhaps as a public company, it might not be a good idea to use the resources of the public company for your private company?"

In his testimony, Musk characterized Tesla employees' work for him at Twitter as "just a voluntary thing." He also said: "This was sort of an after-hours, just if you're interested in evaluating the — helping me evaluate Twitter engineering, that would be nice. It was very short-term. I think it lasted for a few days and it was over."

Musk also said, "I didn't really regard this as using Tesla assets, as I had asked just for a voluntary basis, and I did not specify any number of people. I don't know what the number was, but I don't think it was quite 50. But it was a small number. There's 120,000 people at the company, just to be clear, so this is de minimis."

A Tesla employee told CNBC that most people at the electric vehicle company would be honored if they were asked to work additional hours at other Musk companies. However, they said most would also feel it was impossible to turn down a direct request from Musk without later facing poor performance reviews or other consequences. This person declined to be named because they were not authorized by the company to talk to the press.

In addition to Tesla employees, Musk has also enlisted execs and employees from SpaceX, the reusable rocket and satellite internet services company he founded in 2002, to help him at Twitter. SpaceX is a major U.S. defense contractor whose revenue is derived from contracts with NASA and the U.S. Air Force, among others.

More than a dozen SpaceX employees were authorized to work at Twitter as of early December, including:

• VP of Human Resources Brian Bjelde
• Chief Financial Officer and Head of Strategic Acquisitions Bret Johnsen
• Director of Information Technology Joshua Ursenbach

At least three of Musk's top execs from his tunneling business, The Boring Company, are also authorized to work for him at Twitter as of early December. They are:

• President Steve Davis
• Director of Electrical and Software Engineering Riccardo Biasini
• Chief of Operations Jehn Balajadia

In addition to employees from his other companies, Musk has enlisted longtime friends and investors who have a stake in "Twitter 2.0" under his leadership. Some of those people authorized to work at the company as of early December include:

• Angel investor Jason Calacanis
• DFJ Growth Partner and Founder Randy Glein
• Andreessen Horowitz General Partner Sriram Krishnan (who is a former Twitter employee)
• Sutter Hill Ventures' Managing Director Samuel Pullara
• Craft Ventures' Partner and co-founder David Sacks
• Five people from Valor Equity Partners, including the firm's founder, Antonio Gracias, and Elon Musk's former chief of staff at Tesla and SpaceX, Sam Teller, who is now a venture partner at Valor.

A current Twitter employee told CNBC that Musk has been "flattening" the organizational structure at the company since early November so that many managers have over 20 direct reports each. Most had closer to 10 before the Tesla CEO took over, which left them time for mentoring.

Now, it's also harder for employees to ascertain who is working on what projects within Twitter because Musk's team has eliminated a tool called Birdhouse that was previously used as an internal directory and organizational guide.

Spokespeople from Twitter and Musk's other companies did not immediately respond to requests for comment.