SoftBank, however, stood by Arora, the third-highest paid executive in the world with a pay package of $135 million.
A group of investors of Japanese mobile giant SoftBank has sought probe and possible sacking of its India-born COO Nikesh Arora over potential conflicts of interest tied to his role as an adviser to a private equity firm.
But SoftBank has stood by the Banaras Hindu University- graduate who is seen as heir-apparent to its billionaire founder Masayoshi Son.
New York firm Boies Schiller & Flexner, acting on behalf of unidentified shareholders, wrote to the board questioning Arora's existing role as a senior adviser to private equity firm Silver Lake and alleged past wrongdoing and generally poor business decisions.
Another latter to Sprint Corp, which SoftBank controls, asks for his removal as a director for similar reasons.
SoftBank, however, stood by Arora, the third-highest paid executive in the world with a pay package of $135 million.
He is president & chief operating officer of SoftBank Corp.
Acknowledging receipt of letter from the US law firm, SoftBank in a statement said, "Mr Arora remains a highly valued leader with proven investment abilities and we are confident he will continue to make great contributions at SoftBank in the years ahead."
Son, one of Japan's richest men and the chief executive of SoftBank, backed the former Silicon Valley executive. "I have complete trust in Nikesh and one thousand per cent confidence in him and know he will continue to do great things for SoftBank in the future," Son said in a statement.
Arora, 48, denied allegations as baseless. "I take my fiduciary responsibilities seriously and have acted appropriately and in the best interest of shareholders throughout my tenure at SoftBank and Sprint, just as I have conducted myself throughout my professional life. I am completely confident the allegations in the letter are baseless," he said in a statement.
Arora -- who gave up a high-profile post at Google to join the Japanese firm in 2014 -- last August said he would buy 60 billion yen of the company's shares, worth $483 million at the time to show his confidence in its prospects.
That was the largest insider purchase by an executive in Japan for at least 12 years.
"We can confirm we are in receipt of a letter from a US law firm claiming to represent unidentified shareholders. The letter makes unsubstantiated allegations against Mr Arora," SoftBank said.
"The Board takes its duties seriously and is in the process of reviewing the letter."
The unnamed shareholders have alleged conflicts of interest, poor performance in making investments for SoftBank and excessive compensation at the company without sufficient disclosure.
The conflict-of-interest allegations center on Arora's role as a senior adviser at Silver Lake, a position he has held since 2007 when he worked at Google.
SoftBank said that it is aware of Arora's involvement with Silver Lake and takes care to thoroughly vet any potential conflicts.
