A billionaire associated with Five Hour Energy is being investigated in a Swiss bank tax probe, according to a source.

• The Senate committee chairman wrote in a letter to Pictet's managing partner that billionaire Five Hour Energy entrepreneur Manoj Bhargava allegedly had undeclared bank accounts worth hundreds of millions of dollars at the Swiss bank.
• CNBC's reporting linked the letter to Bhargava, even though it was only identified as "Person 1."
• The allegations against Bhargava and another Person 2, if true, could result in the largest individual FBAR penalty in U.S. history, according to Sen. Ron Wyden, D-Ore.

According to Senator Ron Wyden, D-Ore., Manoj Bhargava, the billionaire founder of Five Hour Energy, allegedly had undeclared bank accounts worth hundreds of millions of dollars at Swiss bank Pictet.

The investigation committee's letter did not mention Bhargava by name, referring to him as "Person 1." However, a source close to the investigation and documents reviewed by CNBC indicate that Bhargava was the account holder in question.

Wyden claims to have obtained documents regarding an alleged plan to evade US tax on a significant portion of his wealth, which was primarily generated through the sale of highly caffeinated liquid in retail stores nationwide.

Wyden wrote that Person 1 has been a Pictet client for at least fifteen years, according to records reviewed by the Committee.

The account linked to Bhargava, which was reported by CNBC, received a deposit of $255 million in 2013, but was later zeroed out at the end of that year.

Bhargava allegedly retained control over the funds despite Person 1 transferring them to a Bahamas entity nominally owned by Person 2, as suggested by the documents.

Bryan C. Skarlatos, an attorney for Bhargava, declined to comment on the letter when asked by CNBC.

Pictet's spokesperson directed CNBC to a statement made in December regarding its resolution with the Department of Justice over its American clients. The statement stated, "This resolution was a result of Pictet's extensive cooperation with US authorities, in accordance with Swiss law. The DOJ acknowledges the significant assistance provided by Pictet in the resolution agreement."

Almost $9 billion in assets from 1,109 accounts and 1,236 names was given to the Department of Justice by the bank.

Bhargava allegedly controlled the funds that were in the nominal possession of Person 2, as cited in the Wyden letter.

• Bank statements and correspondence related to Pictet accounts owned by Person 2 or her entities were delivered to Person 1 at his business address.
• Bankers at Pictet discussed Person 2's accounts with Person 1's representatives.
• Despite having zero balances in his accounts, Person 1 was visited by bankers twice a year to discuss business.

The Swiss accounts that Bhargava (Person 1) reported to the Internal Revenue Service were not under his control, according to foreign bank account reports.

Bhargava, a U.S. citizen born in India, conducts business in the suburbs of Detroit and is required to disclose his foreign bank accounts to the IRS and pay related taxes.

In less than a decade, Bhargava pushed the $1 billion sales mark for 5 Hour Energy, which he created in 2003.

He is a member of The Giving Pledge, a charitable campaign founded by billionaires Warren Buffett and Bill Gates, which involves making a non-binding promise to donate the majority of one's wealth to philanthropy.

On The Giving Pledge website, Bhargava stated that he intended to donate 90% of his wealth to charitable causes.

"Using wealth to serve others is the only intelligent option, as personal consumption choices are either pointless or detrimental."

The allegations against Bhargava and Person 2, if true, could potentially result in the largest individual FBAR penalty in US history, surpassing the current record of $100 million.

Bhargava's transactions with Person 2 were questioned by Wyden's letter due to the fact pattern within the Swiss bank.

Despite no longer being the officially listed account holder or possessing signatory authority over the funds sent to Person 2's accounts, Pictet continued to direct inquiries and paperwork concerning the funds to Person 1 and his advisors, as stated by Wyden.

The Senate Finance Committee was informed of claims that in 2014, some of the bank's legal staff and external lawyers advised Person 1 to make a self-report to the IRS regarding an account, but Person 1 did not comply.

A criminal investigation into the matter has been launched by federal agents from the Department of Justice and IRS Criminal Investigation, according to Wyden.

It was not clear Thursday whether any such investigation remained open.