Hungary asked Brussels on Thursday to lift the immunity of an MEP from the far-right Jobbik party, amid reports he was being investigated on allegations of spying for Russia.
"Hungary's chief prosecutor Peter Polt has turned to European Parliament President Martin Schulz to suspend the parliamentary rights of MEP Bela Kovacs," Polt's spokesman Geza Fazekas told AFP.
"A serious crime investigation has been launched which could lead to a prison sentence of between two and eight years," he added about the reasons for the request, without providing further information.
The daily Magyar Nemzet had earlier cited unnamed sources in Hungary's intelligence agency as saying the 54-year-old Kovacs was being investigated at home for "espionage against European Union institutions".
They said Kovacs regularly met in a "conspiratorial manner" with Russian diplomats, and travelled once a month to Moscow.
Kovacs himself however called the allegations a "smear campaign" to damage Jobbik's prospects in the upcoming election, at a press conference in Budapest on Thursday.
"I've never been a member of any security service, Hungarian or foreign," he insisted.
A spokesman for Schulz, Armin Machmer, confirmed to Hungarian news agency MTI that Schulz had received the request from Budapest but said the case would only be considered if Kovacs was reelected.
Kovacs is third on Jobbik's candidate list for the European Parliament elections on May 25.