Tesla CEO Elon Musk is facing mounting pressure from regulators and critics since his tweet last week to take the company private and the fallout that has followed.

The Wall Street Journal reported Wednesday (subscription required) that Tesla's board has received subpoenas from the Securities and Exchange Commission regarding Musk's Tweet about taking the company private. The report cites "a person familiar with the matter."

Last Wednesday, the Journal reported that the SEC began initial inquiries into Musk's tweets.

The concern is whether Musk indeed had "funding secured" for a private takeover bid as his Tweet said, and how secure that funding may have been.

Elon Musk at Tesla Model 3 reveal

Elon Musk at Tesla Model 3 reveal

In a letter to employees and shareholders Monday, Musk said he had held talks with the Saudi sovereign wealth fund about taking the company private. In it, he said that the managing director of the Saudi fund had "expressed his support for funding a going private transaction," and that Musk understood no other decisionmakers were needed.

He did not indicate that the fund had conducted the due diligence required to make such an investment, which would include an investigation by the federal Committee on Foreign Investment in the U.S. (CFIUS), according to a Bloomberg report.

The CFIUS would routinely be required to sign off on any large foreign investment in any large U.S. manufacturer.

On Tuesday, Musk tweeted that Tesla had hired investment advisors from Goldman Sachs and Silver Lake Capital to help facilitate the buyout. It was not clear whether they might be advising Musk on the SEC investigation. Goldman Sachs confirmed to CNN on Wednesday that it is working with Tesla.

"Whistleblower" photos

At the same time former employee Martin Tripp, whom Musk has called a "saboteur" but who has claimed whistleblower status with the SEC, briefly tweeted out several photos purportedly showing damaged batteries, before and after they were repaired, toxic waste at the company's battery Gigafactory in Nevada (where he worked), and identifying VIN numbers which he alleges contain damaged battery modules.

Tripp's Twitter account was closed within hours of the posting.

In reference to Tripp's allegations, a Tesla spokewoman in an emailed statement told Green Car Reports: "These claims are false and Mr. Tripp does not even have personal knowledge about the safety claims that he is making. No punctured cells have ever been used in any Model 3 vehicles in any way, and all VINs that have been identified have safe batteries. Notably, there have been zero battery safety issues in any Model 3."