Gauselmann, which manufactures gaming machines and operates gambling halls, allegedly made financial contributions to parties across the political spectrum – from the conservative Union bloc to the Social Democrats, Free Liberals and the Greens.
The newspaper reported that company CEO Paul Gauselmann required his executives make regular contributions, which totalled up to €70,000 in parliamentary election years.
The contributions from the company do not show up in the parties' contribution reports since only donations from individuals or companies over €10,000 have to be made public.
Martin Morlok, a leading expert on political parties and legal issues, called the donation practices an "ingenious system," that violated standards of political transparency.
Gauselmann has rejected that accusation, saying the donation levels were determined by the amount that his family and managers could legal write off from their taxes.