Schneider-Ammann headed Ammann, a construction equipment company, until he was elected to the federal government in 2010 as a member of the centre-right Liberal party.
Der Bund and Tages Anzeiger reported on Wednesday that Ammann used a Luxembourg-based firm, Manilux SA, as a private bank for the company, providing lines of credit for its international operations.
Schneider-Ammann was a member of the board of Manilux from 1992 to 2007, and its chairman for several years, the newspapers said.
Manilux managed sums up to 230 million francs that were not subjected to Swiss taxes, the journals said, citing tax experts.
Yet the company employed no one in Luxembourg, suggesting the subsidiary was just a shell company used to evade taxes, according to the reports.
The development comes after authorities in Bern said they were investigating Ammann’s activities in the wake of concerns about a subsidiary it operated in Jersey, the Channel Islands tax haven.
The Rundschau public affairs programme on SRF, the German-language state TV, reported last week that the Ammann Group managed assets of 264 million francs through the Jerfin subsidiary between 1996 and 2009.
Schneider-Ammann and Ammann maintain that they acted according to the law and in complete transparency.