Labour minister Eric Woerth is at the centre of the allegations Prosecutors have launched an investigation into claims of illegal campaign funding for French President Nicolas Sarkozy, officials say.
The move follows allegations by a former accountant for France's richest woman, Liliane Bettencourt.
The accountant reportedly told police she was involved in channelling 150,000 euros (£124,000) to Mr Sarkozy's presidential campaign in 2007.
Mr Sarkozy dismissed claims surrounding the case as a "smear".
The money was to be handed over to Eric Woerth, who ran Mr Sarkozy's campaign, according to Mrs Bettencourt's former accountant, Claire Thibout.
Her allegations were reported by the French website Mediapart after she made a statement to police on Monday.
Mr Sarkozy has been facing growing pressure over the affair, which is linked to a trial over the 87-year-old Mrs Bettencourt's estimated 17bn euro fortune that opened briefly last week before being adjourned.
Mr Woerth, who has denied the allegations, is currently minister for labour in Mr Sarkozy's government and is leading efforts to push through a major pension reform.
In a television interview on Tuesday he denounced what he called "a political plot orchestrated by the Socialist Party".
Earlier that day, opposition MPs had walked out of the French parliament after a minister criticised them for repeatedly asking about the allegations.
BBC
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