France's Economy Minister Emmanuel Macron will have to pay back-taxes after authorities found he had undervalued a family
property, two French media outlets have claimed.

The former Rothschild banker, who has sought to position himself as a possible candidate for next year's presidential election, denied being the target of any tax demand.

“I am up to date with the tax administration and the high authority on transparency in public life,” he said during a visit to a factory in northern France.

News site Mediapart and newspaper Canard Enchaine claim a tax audit has found that Macron is liable for a tax on the rich which affects anyone with property worth at least €1.3 million ($1.4 million).

The Canard Enchaine said discussions with the tax authority had lasted more than 18 months and hinged on the value of his wife's home in northern France.

The home was valued by the tax office at €1.4 million, rather than the €1.2 million stated by the minister.

The minister “has finally admitted that he should pay (the tax)” and resubmitted his tax declaration for 2013 and 2014, Mediapart said, adding that the increased bill and penalties would probably amount to less than €10,000.

Quizzed on Tuesday, Macron said he was in favour of transparency but also respected privacy over tax matters, “like all citizens”.

He claimed there had been a concerted campaign in recent weeks to dig up dirt “in order to destabilise me”.

The minister made waves last month by setting up his own political movement, “En Marche” (On the Move), seen as a possible first step towards a run at the presidency in place of the deeply unpopular Francois Hollande in 2017.

Cabinet colleagues have called for him to get into line.

Macron's office did not comment when contacted by AFP, but one close ally, Socialist MP Pascal Terrasse, said he was “the target of an attack because he is shaking things up”.

Macron earned nearly 2.4 million euros during his time at Rothschild between 2011 and 2012, according to the transparency body.