NYSE Euronext (NYX) and Deutsche Boerse have extended the deadline to complete their planned merger to March 31 in a last ditch effort to persuade European regulatory officials to back the pricey $9 billion deal, according to Reuters.

The stock exchanges, which both agreed to the merger on Feb. 14, have been struggling over the last year to get antitrust backing from officials in Europe for the merger.

The extension comes after months of unsuccessful lobbying by merger partners who had hoped to convince European antitrust authorities to approve the combination, its biggest and final hurdle in the deal.

In September, a German regulatory authority approved the merger in what had seemingly been a step forward for NYSE Euronext and Deutsche Boerse, however that nod has yet to sway broader regulatory bodies in Europe, which fear the merged entity would have a monopoly in European futures and options.

The exchanges offered concessions in November to try to appease regulators, including spinning off parts of NYSE’s futures trading business and offering open access to Deutsche Boerse’s clearing unit to rival exchanges, but those efforts were rejected.

Two weeks ago, the exchanges offered further concessions, including an assurance that derivatives trading fees would be capped for three years after the deal, but European regulators still showed no signs of lowering their guard.

The European Commission, which is the last hurdle after both exchanges' shareholders and the  U.S. antitrust authority approved the deal, is expected to make a decision by Feb. 9.

Last week, when executives realized the Dec. 31 deadline would be missed, the companies told the Securities and Exchange Commission they would exercise their right to extend the initial termination deadline to March 31.

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