Based on all-you-can-eat restaurants, the brothels are offering customers the chance to sleep with as many prostitutes as they like for a single fee.
The owners have also offered rebates for pensioners, the unemployed and those on welfare. Some have offered discounts to taxi drivers and rubbish collectors on the 15th of the month, which is close to pay day.
However, it is the flat-rate deals that have attracted particular controversy in a country where prostitution is legal, reports The Telegraph.
Conservative politicians have vented anger and disgust at the innovation.
In a bid to put an end to such offers, the politicians have also ordered a wave of police raids on sex clubs.
"This is an outrageous violation of human dignity," Heribert Rech, the Baden-Wurttemberg interior minister, told The Times.
"So-called flat-rate sex is an immoral development which cannot be tolerated in our society," Rech added.