Slaughter and May's best friends in Europe, Uría Menéndez and Bonelli Erede Pappalardo, have won the chief instructions on Europe's biggest M&A deal of the year so far.
The proposed €25bn (£17.21bn) tie-up between Spanish highway company Abertis Infraestructuras and Italian counterpart Autostrade will create one of the world's largest motorway companies, with 20,000 staff in 16 countries.
But the deal has hit a hitch in the form of Autostrade chief executive Vito Gamberale, who has sent a letter to chairman Gian Maria Gros Pietro to express concerns over the deal.
Although he voted in favour of the merger, he says he was not informed of discussions between Abertis and Autostrade's largest shareholder Schemaventotto, which will own around a quarter of the new company. Schemaventotto is controlled by the Benetton family.
The Autostrade board will meet early this week to discuss the issue.
Corporate partners Mariacristina Storchi and Roberto Cera and finance specialist Andrea Novarese from Bonelli are advising Autostrade. Advising Abertis are Uría partners Coloma Armero and Jose Luis Vasquez, with Enrico Vitali and Marcello Valenti at Italian firm Vitali Romagnoli Piccardi & Associati helping out on tax matters.
No lawyers wished to comment on the deal before the meeting.