Reacting to widespread although still unconfirmed reports that European Union Competition Commissioner Joaquín Almunia (pictured left) will recommend that the European Commission reject the proposed NYSE Euronext-Deutsche Börse AG merger, NYSE chief executive Duncan Niederauer (right) told his employees that the companies will "press our case directly" with the other 26 commissioners. They hope to convince them to overrule their Spanish colleague.

But Brussels hands believe that the chance of a reversal by the full EU executive arm, the so-called college of commissioners, is slim to none. Overruling the competition commissioner is not unprecedented, but it is very rare. After media reports signalled the thinking of the competition team, experts say, an EU executive reversal would be seen as an especially political move, exposing the Commission to both criticism and court challenges.

With less than a month to go until the EC closes its in-depth investigation of the union, openly strong-arming the full Commission is "a heavy-handed approach," said George Metaxas, a competition partner with Brussels law firm Oswell & Vahida. "It will only make it even more difficult for Almunia to clear the deal even if he wanted to, and even if there are last-minute concessions. In fact, it's the best way to make sure he will not clear it.

"If I were NYSE or Deutsche Börse," Metaxas continued, "I would try to offer some additional and meaningful commitments, announce this to the world, and then lobby hard on the political front -- but only behind the scenes and very discreetly. They seem to be doing the exact opposite."

Who are the 27 commissioners who make up the crucial college of voters? France's representative, Michel Barnier, the internal markets chief, might be the most sympathetic to the exchanges' arguments. He has been a vocal advocate of strengthening Europe's financial centers. Most of the commissioners are far from financial experts: Danish climate chief Connie Hedegaard; Cypriot education and multiculturalism commissioner Androulla Vassiliou; German energy commissioner Günther Oettinger; Estonian transport commissioner Slim Kallas, among others. They will not find it easy to dismiss the recommendation of the competition commissioner.

If Almunia has rejected the exchange operators' argument that derivatives trading should be viewed as one global market (not a European market) that includes listed and over-the-counter trading, it may be impossible for the deal to win clearance.

There is no doubt that the merger proposal is Almunia's first controversial case since he succeeded the colorful Neelie Kroes and the scholarly, much-admired Mario Monti. Said London-based consultant Hirander Misra, "this is exactly the kind of scenario where a tough call could massively strengthen his reputation and stature."

Niederauer and Deutsche Börse CEO Reto Francioni would say it's the wrong call. But they won't have the final word.