The dispute brings into question the sway that the Treasury has over strategic state-backed companies in which it shares the ownership with increasingly vocal institutional investors.

Investor Covalis Capital has argued for more shareholder democracy, saying the Treasury should not be able to dictate choices in a publicly listed company.

Enel, which is also one of Europe's largest utilities, has sought to position itself as a leading developer of renewable energy. However, its debt has risen and it has decided to focus its activities on six countries, including Italy, Spain and the United States.

The outcome of Wednesday's vote is difficult to call and the shareholder meeting, due to start at 1200 GMT, could extend deep into the evening.

The Treasury has a stake of 23.6% in Enel and is confident to win board seats for its slate of six nominees, who include its CEO candidate Flavio Cattaneo, currently vice-president of high-speed rail operator Italo.

The remaining three board seats will likely be divided between London-based Covalis and institutional investor group Assogestioni.

The vote for the chairman is expected to be close. It is a straight fight between Treasury candidate Paolo Scaroni, who is a former CEO of both Enel and energy company Eni and who is currently the chairman of soccer club AC Milan, and Covalis candidate Marco Mazzucchelli.

Covalis argues that Enel needs an independent figure, such as former top banker Mazzucchelli, to oversee its business and may try to reopen the choice of chief executive if its candidate for chairman is successful.

(Reporting by Francesca Landini and Keith Weir; Editing by Sharon Singleton)