“The credibility of our institutions is at stake,” said Manon Aubry, co-chair of The Left in the European Parliament.

If proven, the allegations would set in motion the biggest scandal to engulf Brussels since the mass resignation of the Jacques Santer Commission in 1999 over allegations of financial mismanagement.

Police detained former Commission Vice President Federica Mogherini, a center-left Italian politician who headed the EU’s foreign policy wing, the European External Action Service, from 2014-2019, and Stefano Sannino, an Italian civil servant who was the EEAS secretary-general from 2021 until he was replaced earlier this year.

The European Public Prosecutor’s Office said it had “strong suspicions” that a 2021-2022 tendering process to set up a diplomatic academy attached to the College of Europe, where Mogherini is rector, hadn’t been fair and that the facts, if proven, “could constitute procurement fraud, corruption, conflict of interest and violation of professional secrecy.”

The saga looks set to inflame already strained relations between von der Leyen and the current boss of the EEAS, EU High Representative Kaja Kallas, four EU officials told POLITICO. Earlier this year Sannino left his secretary-general job and took up a prominent role in von der Leyen’s Commission.

An EU official defended von der Leyen, instead blaming the EEAS, an autonomous service under the EU treaties that operates under the bloc’s high representative, Kallas — who is one of the 27 European commissioners.