With a unanimous vote, the European Parliament decided on Monday (12 March) to launch a probe into a reported power grab within the European Commission amid broader questions over the institution's integrity.

The task into how the German 47-year old Martin Selmayr, EU commission president Jean-Claude Juncker's chief of staff, became the institution's top administrator last month, has fallen into the lap of the parliament's powerful budgetary control committee.

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The move was made before a heated debate at the parliement's plenary session in Strasbourg between the EU commission and MEPs.

The budgetary control committee is presided over by German centre-right deputy Ingeborg Graessle.

"I don't think that there is any doubt the Mr Selmayr is competent, I think this is the most important thing when you are looking at a promotions," said Graessle who is from the EPP, Juncker's political family.

But Francoise Grossetete, a French MEP who is the EPP group's vice president, described the Selmayr move as an affront to transparency that risks undermining the EU commission.

"Appointments mustn't mean adopting powers in a higher administration thanks to arrangement among friends or to the detriment of people lower down," she said, comparing Selmayr's promotion to a "mystification worthy of the Chinese Communist Party".

Her counterpart from Hungary, Gyorgy Schopflin, echoed similar statements.

"When it suits the commission, it ignores the rules, meaning the rule of law," said the MEP from the Fidesz party of Hungarian prime minister Viktor Orban.

Some MEPs have pointed out that the Selmayr case was important because the EU commission is supposed to maintain high standards, and that its authority over Poland and Hungary on matters of rule of law could be weakened.

Such observations are feeding into further anti-EU rhetoric by firebrand EU politicians and populists, MEPs said.

Last week, Hungary's government spokesperson talked of EU double standards. In Monday's plenary, far-right MEPs like British eurosceptic Nigel Farage railed against the EU.

The uproar has attained fever pitch following Selmayr's appointment, personally announced by Juncker at a press conference in Brussels, given contradictory versions by the EU commission on how he landed the job.

Matters were made worse by a gaffe in the EU commission's communications service, which published a photo of Selmayr captioned "secretary general" one week before Juncker's announcement. It later deleted the caption, but not before a journalist had seen and reported the mistake.

"The commission will have to choose what is more important, the career of Mr Selmayr or the credibility of the European Union," said Dutch liberal Sophia in't Veld on Monday.

Green Belgian MEP Philippe Lamberts took it further and accused Selmayr of "moving forward with authoritarian centralisation".

Placing a German national in the top EU commission civil post has also raised tensions given similar top administrative jobs at the EU institutions are are also filled by Germans.

Budget commissioner Guenther Oettinger, also from Germany, appeared to skirt explanations behind the promotion to the plenary, which only irked MEPs across party lines even more.

Oettinger said Selmayr had all the qualifications to take on the tasks of the secretary general. He repeated several times that Selmayr was "100 percent suitable" for the post, that he was a committed European, and a good lawyer.

"All decisions, including the decision of the new secretary general, were unanimously agreed by the college of commissioners," he said.

But minutes of the college of commissioners meeting reveal Selmayr's promotion had been rushed, casting doubt over how the vacancy was filled and why other candidates never came forward despite earlier assurances that they would.

In his closing remarks, Oettinger refuted claims that he treated the MEPs as children and that the EU commission had any plans to grant generous pension packages to departing commissioners that included personal assistants and cars.

"It's fake news," he said of the reported pension scheme.

The European Parliament is set to vote on a resolution on the matter in April following the budgetary control committee probe. The EU Ombudswoman, Emily O'Reilly is also looking into the matter.