BUDAPEST (Reuters) - Hungary’s main opposition party would be unable to compete at an election next April if state auditors impose a heavy fine in a campaign finance case, a vice chairman for the nationalist Jobbik party told Reuters on Thursday.

The party, which was once on the far right but has moved toward the center in recent years, lags far behind the ruling party Fidesz, according to opinion polls.

The case could hurt Jobbik’s bid to take the political center ground from the populist and nativist Fidesz party of Prime Minister Viktor Orban, who has ruled Hungary since 2010.

Jobbik should pay a fine of 331 million forints ($1.24 million), equal to a price advantage it received illegally for a billboard campaign. Its annual state subsidy should also be cut by the same sum as a penalty, the auditors said on Wednesday in a preliminary finding.

Jobbik denies wrongdoing and has 15 days to respond to the findings. The auditor, called ASZ, will deliver a final ruling in a few weeks and Jobbik would then have to pay the fine even if it challenges the decision in court.

The penalties are more than Jobbik’s 476 million forint annual state subsidy, which is the party’s largest source of funding as it receives only small contributions from donors, Jobbik vice chairman Janos Volner said.

“This case has been so absurd that anything is possible,” he said, adding that the inquiry could be a pretext to try to dissolve the party. “They will shake us down for every last penny we have,” he told Reuters by phone.

The auditor is independent and non-political, said its spokesman Balint Nemeth.

ASZ Chairman Laszlo Domokos is a former Fidesz lawmaker while Chief Prosecutor Peter Polt is a former Fidesz member twice appointed to his post by Fidesz-dominated parliaments.

On Wednesday, prosecutors also pressed espionage charges against Jobbik European Parliament member Bela Kovacs, who subsequently quit the party.

In its ad campaign Jobbik accused Orban and some of his associates of corruption. The party used billboards owned by a tycoon named Lajos Simicska for the campaign. Simicska was once a key ally of Orban who has since become a supporter of Jobbik.

In stormy debates with Jobbik party leader Gabor Vona in parliament, Orban has repeatedly said Jobbik has been hijacked by Simicska and accused it of doing his bidding. Jobbik and Simicska deny this.

Fidesz restricted the use of privately-owned billboards by political parties in a recent law. Jobbik then bought more than 1,000 billboards outright. The party has declined to detail the sources it used for that deal.

($1 = 266.53 forints)