Russia's main investigative body claimed Wednesday that Alexei Navalny, the charismatic leader of protests against President Vladimir Putin, illegally obtained his licence to practise law.
Investigators said in a statement that the opposition leader and one of Russia's most popular bloggers gave "inaccurate" information to the bar.
It was unclear which laws Navalny allegedly broke and what charges he may face.
Navalny, already the subject of several criminal probes, responded on Twitter by calling the allegations "complete rubbish".
The investigators said that Navalny claimed to the bar that he had a few years experience as a deputy director in charge of legal affairs at a company but that in fact this was his own company where he was general director.
They said he also exaggerated the length of time he worked there and alleged that he refused to testify when asked about the allegations.
The opposition leader wrote on his Livejournal blog that he briefly met with an investigator Wednesday regarding one of the probes, but his lawyer licence was not discussed. He said Wednesday's statement apparently referred to an interrogation dating back to August 2012.
"As to the substance of the allegations, I have been saying for a year... you have checked everything, you have seized all of my documents, so go complain to the bar," Navalny wrote.
"So far such complaints have been unsuccessful because they contain complete rubbish."
The investigators' statement echoed nearly verbatim allegations made by a pro-Kremlin blogger last week. Russia's federal channels aired the allegations prominently in their news coverage without getting a comment from Navalny.
The square-jawed lawyer emerged as one of the most popular leaders of mass protests against Putin's return to the Kremlin for a third term, although some liberals oppose him because of his appearances at nationalist rallies.
He built on the following he had gained as a whistle-blowing blogger and minority shareholder campaigner.
The 36-year-old has come under several criminal probes, including one alleging that he caused a loss of 16 million rubles ($525,000) to a regional budget that could put him in jail for up to 10 years.
He has not yet been arrested, unlike many other opposition activists.