EU chief Ursula von der Leyen faces a confidence vote that has little chance of succeeding but has exposed frictions between her backers and complaints about her leadership style.
European lawmakers will vote on the rare challenge pushed by a far-right faction against the European Commission president at around midday in Strasbourg.
Addressing parliament this week, von der Leyen dismissed the no-confidence motion as a conspiracy theory-laden attempt to divide Europe, dismissing its supporters as "anti-vaxxers" and Russian President Vladimir Putin apologists.
She urged lawmakers to renew confidence in her commission, arguing Europe needed to show unity in the face of various challenges, from US trade talks to Russia's war in Ukraine.
The no-confidence motion was initiated by Romanian far-right lawmaker Gheorghe Piperea.
He accuses von der Leyen of a lack of transparency over text messages she sent to the head of the Pfizer pharmaceutical giant when negotiating Covid vaccines.
The commission's failure to release the messages, the focus of multiple court cases, has given weight to critics who accuse its boss of centralised and opaque decision-making.
That is also a growing refrain from the commission chief's traditional allies on the left and centre, who have used the vote to air their grievances.
A major complaint is that von der Leyen's centre-right camp has increasingly teamed up with the far-right to further its agenda, most notably to roll back environmental rules.
Centrist leader Valerie Hayer told parliament this week that von der Leyen's commission was "too centralised and sclerotic" before warning that "nothing can be taken for granted".
"Pfizergate" aside, Romania's Piperea accuses the commission of interfering in his country's recent presidential election, in which pro-European Nicusor Dan narrowly beat EU critic and nationalist George Simion.
That vote came after Romania's constitutional court scrapped an initial ballot over allegations of Russian interference and massive social media promotion of the far-right frontrunner, who was barred from standing again.
Piperea's challenge is unlikely to succeed.
It has support from some groups on the left and part of the far right, including the party of Hungary's nationalist Prime Minister Viktor Orban.
"Time to go," Orban tweeted on Wednesday alongside a photo of von der Leyen.
But Piperea's group, the ECR, is split. Its largest faction, the party of Italian Prime Minister Giorgia Meloni, said it would back the EU chief.
The two largest groups in parliament, the centre-right EPP and the centre-left Socialists and Democrats, have also flatly rejected the challenge, which needs two-thirds of votes cast, representing a majority of all lawmakers to pass.
