MILAN, Sept 15 (Reuters) - Monte dei Paschi di Siena is moving to close 50 branches in line with commitments taken with European Union authorities under its restructuring plan through 2021, a copy of a letter the state-owned bank sent to unions showed on Wednesday.

It was not immediately possible to reach Monte dei Paschi for comment. (Reporting by Valentina Za, editing by Cristina Carlevaro)