Shares in Rupert Murdoch's News Corporation have fallen to a six-month low in New York hit by the ongoing phone-hacking scandal.
Mr Murdoch, his son James and former News International chief executive Rebekah Brooks face questions from a committee of MPs on the controversy that has widened from the Murdoch media empire to Britain's police and government.
British Prime Minister David Cameron has cut short a trade trip to Africa and was due to return late on Tuesday to attend an emergency debate the following day in parliament.
Ratings agency Standard & Poor's has warned that it may cut News Corp's credit rating.
The company's market capitalisation has lost more than $US6 billion in value since the scandal erupted, Reuters reports.
Chase Carey successor?
The international business news agency Bloomberg reports the company is considering elevating chief operating officer Chase Carey to the position of chief executive, to succeed Mr Murdoch, who would remain chairman.
The report says a decision depends on Mr Murdoch's performance before a British parliamentary committee tomorrow morning New Zealand time.
Mr Carey is a 23-year News Corp veteran and long-time Murdoch lieutenant.
Until the phone hacking scandal started escalating, James Murdoch, who is deputy chief operating officer, had been seen as his father's successor.
News Corp was not immediately available to Bloomberg for comment.
However, a board member told Reuters there was no such plan and directors are fully behind Rupert Murdoch.
News Corp's US shares fell 4.3% at $14.96 on Monday on the Nasdaq, after dropping to a two-year low in Sydney.
Analysts say that if the stock continues to slide Mr Murdoch may have no choice but to step aside, the ABC reports.