Montebourg was one of the founding members of the political movement known as the "Nouveau Parti Socialiste" (New Socialist Party). He left to create a new movement within the Socialist Party called "Rénover, Maintenant" (Renewal, Now). He was one of the leading opponents of President Jacques Chirac's immunity from prosecution, especially concerning the corruption scandals in the Paris region. Montebourg also supported reporter Denis Robert for his role in revealing the illegal system of double-accounts maintained by Clearstream, a clearing-house based in Luxembourg. He has also been engaged in a campaign against the rules governing taxation of foreign nationals and banking secrecy of Switzerland.