Vestager is sometimes seen as a potential successor to European Commission President Jean-Claude Juncker | Jose Sena Goulao/EPA Vestager in hot seat as she moves to derail mega-merger Alstom-Siemens deal looks set to be blocked in Brussels, but Paris and Berlin are exerting political pressure.

EU competition chief Margrethe Vestager will face questions on Tuesday from her fellow commissioners over why she is opposing the French and German governments to thwart the creation of a European rail champion.

Vestager is on course to block a landmark merger between France's Alstom and Germany's Siemens even though Paris and Berlin insist that the tie-up is needed to build a European industrial heavyweight to counter state-backed Chinese rivals.

The Danish liberal, who is sometimes seen as a potential successor to European Commission President Jean-Claude Juncker, is set to play a starring role in Tuesday's highly unusual "orientation debate" among commissioners in Strasbourg, where the Franco-German camp is likely to try to exert its influence.

Although Vestager has already crossed swords with fierce adversaries such as the U.S. tech giants Google and Apple, her opposition to the rail merger is a stern test of her department's ability to withstand political pressure from the EU's most powerful states.

EU antitrust enforcers oppose the so-called Railbus deal (think Airbus but with trains). They fear that the companies, by forming a behemoth, would rip off consumers in national markets, where the merged entity would often have an overwhelmingly dominant position.

While standing up to France and Germany could deal a blow to Vestager's own ambitions in Europe, the commissioner is now supported by a formidable group of allies.

“We can’t build those [European corporate] champions by undermining competition,” Vestager said at an event last week in Berlin. “We can’t build them with mergers that harm competition, or by looking the other way when Europe’s businesses break our rules.”

Over the past few days, it is senior figures in the French government who have sought to swing the political momentum back in favor of the Alstom-Siemens merger. Economy Minister Bruno Le Maire insisted that it would be a "political mistake" to block the deal. Prime Minister Edouard Philippe also asked: "Would we be happy with a Europe, in which, in 30 years, it would be right for our children and ourselves to travel in trains built and designed by manufacturers that are not European?”

This French pressure comes on the heels of rare murmurs of protest from German Chancellor Angela Merkel, who has specifically called on Brussels not to allow its competition rules to stand in the way of mergers that can take the battle to Asia. Germany's main business lobby, the BDI, also spoke out in favor of anti-China champions last week.

While standing up to France and Germany could deal a blow to Vestager's own ambitions in Europe, the commissioner is now supported by a formidable group of allies.

On Monday, the European Association of Rail Infrastructure Managers (EIM) sent a letter to Juncker and eight commissioners, including Vestager, opposing the deal.

That industry intervention comes after competition authorities from the U.K., Spain, the Netherlands and Belgium, and Germany also sent letters to the European Commission arguing that Alstom and Siemens have not offered sufficient remedies.

If the French and German governments were to overcome such widespread reservations, policymakers would ask big questions of the Commission's neutrality.

“Commissioner Vestager will brief the College [of Commissioners] on this case indeed, but no decisions will be taken tomorrow ... The aim is to enable a collegiate decision by the deadline [on February 18],” said a person familiar with the matter.

The Strasbourg meeting gives Vestager’s critics some leverage over the decision. Competition experts say such orientation debates are not uncommon as they help the commissioners to test their positions ahead of determining a final official stance on a specific matter. However, it is rare ahead of a merger decision, which underlines the strategic importance of the deal.

As far as her own career prospects are concerned, Vestager is intimating that she might not have too many friends left on the European political stage after May's European Parliament election and the appointment of a new Commission later in the year.

As she told Danish news outlet B.T., “Next year at this time I’m probably unemployed.”

But that may not necessarily be the case. Blocking a big merger often builds a political reputation. To the shock of many international observers, Mario Monti, who later went on to be Italian prime minister, blocked the mega-merger of his time: GE-Honeywell in 2001.

Lili Bayer and Joshua Posaner contributed reporting.

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