The European Parliament in Strasbourg, France | Frederick Florin/AFP via Getty Images Mainstream parties block Euroskeptics from top Parliament posts Some committees suspend voting on leadership positions as pro-EU groups move to exclude far right and populists.

Mainstream, pro-EU political parties in the European Parliament moved aggressively to block Euroskeptic and extremist groups from claiming several prominent committee leadership posts on Wednesday.

That blocking effort enraged anti-establishment forces and potentially put at risk an overall deal on the EU’s future leadership.

One group leader, Ryszard Legutko of the right-wing European Conservatives and Reformists (ECR), pointedly warned that his MEPs were less likely to support the deal on top jobs agreed by European leaders last week after one of their members — former Polish Prime Minister Beata Szydło — was blocked from becoming chairwoman of the Employment and Social Affairs Committee.

Anti-establishment forces, including far-right and extremist groups, gained strength in the recent European election. The new Identity and Democracy (ID) group, a partnership between Matteo Salvini's League in Italy and Marine Le Pen's National Rally in France, is now the fifth-largest group with 73 MEPs — just two fewer than the Greens.

Together, ID and ECR have 135 MEPs, far more than the 108 seats controlled by the liberal-centrist Renew Europe, backed by French President Emmanuel Macron.

But pro-European forces overall control 519 seats and they wielded that muscle Wednesday to deny the insurgent groups several positions, effectively upending the so-called D’Hondt method by which leadership positions are traditionally apportioned among parliamentary groups.

ID had expected to hold the chair of the agriculture committee but its nominee, French MEP Maxette Pirbakas, was blocked by the four pro-EU parties. They instead elected Norbert Lins, a German MEP from the conservative European People’s Party. Pirbakas was then also rejected for two vice chair positions, before voting was suspended for the final spots.

In one of the most bitter stings for the far right, the pro-EU groups also voted down an ID candidate, French MEP Gilles Lebreton of National Rally, who had expected to be chairman of the Committee on Legal Affairs.

Instead, a British liberal, Lucy Nethsingha, was elected to head the panel, which among other responsibilities maintains oversight of the limited parliamentary immunity enjoyed by MEPs. Nethsingha may be out of the Parliament come October 31 after Britain leaves the EU.

József Szájer, an MEP from Hungary’s ruling Fidesz party who chaired the initial vote in the legal affairs committee, had implored colleagues to respect the handshake agreement and the proportional formula.

“I would like to ask you, as the legal affairs committee, to observe the old traditions of the rule of law of our committees and elections, which is based on agreements by political groups," Szájer said. "We have worked with those rules for 40 years, and if those agreements are not upheld, the consequences are unforeseeable.”

But the pro-EU MEPs were unmoved by the request from Szájer. Sylvie Guillaume, a French socialist, accused ID of having transparent motives in seeking to lead the legal affairs committee, known as JURI. “It fools no one that they chose the JURI committee, where parliamentary immunities are waived,” Guillaume said.

When Le Pen was an MEP in 2017, for example, Parliament voted to lift her immunity over pictures she tweeted of Islamic State violence.

While the blocking maneuvers essentially maintained the cordon sanitaire that pro-EU groups have used to limit the power of extremists and nationalists, the rising strength of the anti-establishment groups raises the possibility of a backlash.

Several MEPs, infuriated by the blocking effort, warned of just such reprisal in the months and years ahead.

The Euroskeptics and nationalists currently do not hold any vice presidency position in the Parliament, a remarkable absence from leadership given their overall numbers in the assembly. That means they still have no MEPs to chair plenary sittings nor any representation in the Parliament's "bureau," where the most important decisions on the workings of the Parliament are made.

One Euroskeptic in Parliament accused the pro-EU groups of hypocrisy, by claiming to be defenders of democracy while denying representation to minority parties.

“This is the only parliament in Europe that doesn’t give any minimal guarantee to minorities,” said a senior official from the ID group.

Pro-EU MEPs even moved quickly to disqualify candidates from the EU-critical Fidesz, which is led by Hungarian Prime Minister Viktor Orbán and has been suspended from the EPP’s pan-European party organization, but not the parliamentary group.

The Committee on Civil Liberties failed to elect its full leadership after a center-left coalition blocked a Fidesz candidate for vice chair. Rather than allow the election of Hungarian MEP Balázs Hidvéghi, the pro-EU groups nominated Damien Carême, a French Greens member.

Fidesz was not entirely denied, however: Its MEP Tamás Deutsch won a vice chair position on the budgetary control committee.

The vote against Szydło, Poland’s former prime minister, prompted the fiercest response. After she was voted down, ECR leaders warned their MEPs were far less likely to support the overall cross-party deal on the EU's future leadership including the nomination of German Defense Minister Ursula von der Leyen for Commission president.

“We are incredibly disappointed with the behavior of some MEPs in the employment committee today,” said Legutko, the Polish leader of ECR. “At the European elections, Beata Szydło received the highest number of preference votes in Polish history and one of the highest of any individual across the whole EU. That MEPs in the Parliament’s employment committee would reject her candidacy as chair is an insult to her voters and hardly encourages us to support a cross-party consensus next week.”

Lili Bayer, Laurens Cerulus, Laura Kayali, John Rega and Eddy Wax contributed reporting.