BUDAPEST (Reuters) - Hungary’s State Audit Office (ASZ) has fined the main, nationalist opposition party Jobbik 331.66 million forints ($1.29 million) for an anti-government billboard campaign funded by a wealthy adversary of Prime Minister Viktor Orban.

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Jobbik, which entered parliament in 2010 on a radical far-right agenda, is now projecting a centrist image in a bid to unseat Orban at an election due in April, where his Fidesz looks well-placed to retain power.

Confirming the findings of a preliminary report, Hungary’s State Audit Office (ASZ) said Jobbik had been fined for running an advertising campaign at below market prices.

The ASZ gave Jobbik 15 days to pay the fine, equal to the price advantage the party received illegally for the campaign, which accused Orban and some of his associates of corruption.

The fine amounted to more than two-thirds of Jobbik’s annual state subsidy of 475.8 million forints, and the party said the “court-martial” levy could cripple its election campaign. Jobbik has denied wrongdoing.

Jobbik’s subsidy should also be cut by the same amount as the fine, ASZ spokesman Balint Horvath said. Jobbik used billboards owned by tycoon Lajos Simicska, an estranged Orban ally who has since become a supporter of the far right.

Orban says Simicska hijacked Jobbik. Both the party and the tycoon deny this.

Officials at the State Treasury and at Jobbik were not immediately available for comment.

Jobbik received public funds worth nearly a billion forints in 2015 and 2016. The ASZ said Jobbik’s finances over that period were not sufficiently transparent.

The ASZ, which is led by ex-Fidesz lawmaker Laszlo Domokos, has rejected accusations of politicking against Orban’s foes. It said the investigation was part of a regular biennial review of parties that receive public funding.

A rally last month against the crackdown drew about a thousand Jobbik supporters, though the turnout fell well short of similar demonstrations over the past year.

Fidesz commanded 39 percent of all voters in November, according to a survey by pollster Median published in the weekly HVG. Jobbik was backed by 11 percent, while the Socialists were a distant third with 7 percent.