"Law enforcement officers are meeting with the company's management," a source said, adding that the company is cooperating.
The Russian Federal Tax Service filed suit against PwC in December 2006, accusing the auditor of covering up Yukos's illegal financial schemes and of drawing up two different audit reports.
The tax service is seeking to invalidate Yukos-PwC contracts for 2002-2004 and to charge $480,000 from PwC. Tax authorities said Yukos failed to correct violations discovered in 2002 in the following two years.
"The company continued to illegally transfer money to the Production Development Financial Support Fund in 2003-04. Nor did the company start mentioning its profitless operations with bonds in its financial reports," the tax service said.
Tax officials also said that, despite the violations, PwC confirmed that Yukos's financial operations in 2003-04 were in full compliance with Russian legislation.
In 2005, another auditor, Horwath, refused to approve the oil company's financial report, the tax authorities said, adding that it was further evidence of PwC's involvement in Yukos's gray operations.
PwC denies the tax authorities' accusations, saying the management of a company, not an auditor, is responsible for financial decisions.
PwC also said its report on Yukos contained an amendment highlighting the revealed irregularities, which PwC also included in a written statement recommending that the company review its operations.