Some 700 officers searched brothels in four states on suspicion that the establishments were employing foreign prostitutes without work visas and withholding their social benefits.

The flat-rate bordellos – doing business based on the slogan, “Sex with all of the women, as long as you want, as often as you want, and how you want” – have come under fire by politicians and human rights advocates in recent weeks.

One such bordello in Fellbach, singled out for criticism in early July by the mayor, was closed due to poor hygienic conditions. Massage tables and other surfaces were reportedly so dirty that they were a health hazard.

“Furthermore the hot tub was in a very bad hygienic state and food was stored in unacceptable conditions,” a police statement said.

Police startled 176 male guests and 89 female sex workers at the Fellbach bordello, finding one case of suspected forced prostitution. Ten people were arrested, police said.

Some 37 men and 27 women were found at a flat-rate brothel in Heidelberg, which police also closed due to poor hygiene.

Two other establishments were searched in Wuppertal and in Berlin’s Schönefeld district, but no arrests were made, police said.