Italian auto maker Fiat (FIA.MI) will sign a preliminary agreement to buy Carrozzeria Bertone on Thursday, trade union sources said on Tuesday.

At the beginning of August the Industry Ministry authorized the sale of the troubled Turin-based car bodywork company to Fiat.

Fiat will sign the accord for Carrozzeria Bertone with special administrators, the sources said.

(Reporting by Gianni Montani, writing by Stephen Jewkes)