Hungarian MEP Istvan Ujhelyi has called on Donald Tusk to step down as President of the European Council following comments he made about Hungary's Prime Minister Viktor Orbán.
The Socialist member said Tusk was "shockingly permissive" towards what Orbán represents.
Orbán has been a figure of controversy since he became Prime Minister for the second time in 2010, most recently over plans to send out eight million questionnaires on whether Hungarians agreed that immigrants endanger their livelihoods and spread terrorism.
He has also suggested the reintroducing of the death penalty should be on the country's agenda.
In a speech on Monday marking the 40th anniversary of the founding of the European People's Party (EPP), Tusk stressed that he was "proud" to be in the same party with Orbán, underlining that the EPP "must realise that the views of Angela Merkel and [Viktor] Orbán are compatible with each other."
His comments sparked criticism from Ujhelyi, a Vice-Chair of the European Parliament's transport committee, who said, "It is now clear that Tusk is entirely unsuitable to fulfil his duties as President of the European Council and therefore should step down from his position immediately."
The deputy said he had called for an official inquiry into Tusk and demanded that the former Polish Prime Minister is "clear about his stance regarding the politics of Orbán."
Ujhelyi said, "Orbán and his Fidesz party take pleasure in trampling on European values and agreements, while building an increasingly autocratic, illiberal regime stripped of any sensible system of checks and balances. The Constitutional Court has become a caricature of itself filled with party lackeys.
"The Chief Prosecutor, the President of the State Audit, or the Chairman of the National Bank are all irremovable, servile henchmen of Orbán's nepotistic system, former party cadres who are loyal only to the Prime Minister." In his letter to Tusk he asks, "Are you really proud of that, Mr President?"
He goes on, "Mafia-like circles have stolen the agricultural lands from ordinary Hungarians, and every Eurocent of EU support ends up in the pockets of shady oligarchs close to the Prime Minister. In the meantime, Orbán is waging a freedom fight against Europe from EU money as well. Are you really proud of that, Mr President?"
The MEP also reminds Tusk that it was also Orbán, the "Christian-democrat" , who started a "huge billboard hate-campaign against refugees, who bussed thousands of them to neighbouring countries instead of complying with applicable European regulations, then deliberately sabotaged efforts to find a common solution."
He said, "As a devoted admirer of illiberalism, he cosies up to Vladimir Putin and works on the disintegration of the European Union on a daily basis. Are you really proud of that, Mr President?"
The MEP ended, "The darkest years of Europe resulted from the inaction of weak leaders who refused to confront with dangerous tendencies. A responsible leader who wants to see the European project prevail simply cannot be proud to be in the same party with an illiberal despot.
"A reasonable politician who wants to build a strong European Union based on solidarity cannot legitimise someone whose goals are the exact opposite, or he will become the member of the same club that wants to see Europe burn."