Russian prosecutors are to bring charges of money laundering against Mikhail Khodorkovsky, the former boss of oil firm Yukos.
Prosecutors want Mr Khodorkovsky to get 10 years in jail if found guilty
A spokeswoman for the Prosecutor General's office said the charges would involve "laundering to the tune of billions of roubles".
Mr Khodorkovsky is currently awaiting the verdict of a trail on fraud and tax evasion charges, set for 16 May.
He faces up to 10 years in jail, but has always proclaimed his innocence.
Many analysts say the trial is politically motivated and that Mr Khodorkovsky is being punished for his political ambition.
Before he was arrested by Russian authorities in October 2003, he had angered the Kremlin by starting to fund opposition political parties.
Mr Khodorkovsky is currently standing trial with his associate Platon Lebedev.
The spokeswoman for the Prosecutor General's office said the money laundering charges would also apply to Mr Lebedev.
Yuri Schmidt, a lawyer for Mr Khodorkovsky, questioned why details of the proposed money laundering charges were being released just days before the verdict in the fraud and tax evasion case.
"The fact that this is done on the eve of the verdict is very strange and in my opinion is a form of pressuring the judge," said Mr Schmidt.
"There is no procedural necessity for the prosecutor's office to make this announcement now."
Mr Khodorkovsky has been in prison since October 2003 and during that time, the state has pursued Yukos for $27.5bn (£15bn) in back taxes.
When Yukos could not pay this last year, its main oil producing subsidiary Yuganskneftegas (Yugansk) was forcibly sold off.
Yugansk eventually ended up in the hands of Russian state oil firm Rosneft.
Rosneft is now suing Yukos - on behalf of Yugansk - for a total of $13bn in unpaid taxes, unpaid oil supplies and lost profits.
On Friday, a Moscow court upheld a $2.24bn claim by Rosneft against Yukos for not paying Yugansk for certain oil supplies.
"We are pleased with the decision and we are going to wait for other court rulings before taking further steps," a Rosneft spokesman said.
Some commentators believe Rosneft may push for Yukos to go into bankruptcy as a precursor to enabling the Kremlin to take control of Yukos' remaining assets.
Yukos' shares fell by close to 11% on the news.