It is one of various singles parties run since 1995 by "Caravans of Women", a group that says it aims to curb rural depopulation by hooking up couples from different parts of Spain.
The Hotel Romero in the southwestern town of Merida sparked outrage from womens' rights defenders by a poster for its first "Caravan" party with a cartoon of pouting party girls on a bus.
A petition on change.org branded the event "degrading and objectifying" saying it encouraged "sexist stereotypes".
It demanded the hotel apologise for "presenting women as a lure, as a mere object of merchandise".
This tweet from Angelese Martin d Pra slammed the caravan as "Humiliating and insulting".
The hotel's manager Jose Romero insisted: "What we are doing is not something to harm women, quite the contrary -- it is a tool to help people meet other people with the same needs."
For the event scheduled on April 18, the hotel is charging 55 local men 50 euros (54 dollars) to spend an afternoon and evening with 55 women bussed in from Madrid, 175 miles (280 kilometres) away.
The women pay 20 euros to cover their coach fare and return to Madrid after the hotel disco shuts down about 3:00 am, said Manolo Gozalo, the Madrid-based coordinator of Caravans of Women.
He denied being a "pimp", insisting it was no more than an event for singles to meet. He claimed his association has helped 120 couples get together since it started the "Caravans" 20 years ago.
"That the woman pays less so that there is a bit of atmosphere -- if that is sexist, well then it is sexist, but it is what has always been done," he told AFP.
Caravans of Women says it has a mission of "rural repopulation" in Spain, which has seen large-scale migration from the countryside to the cities over the decades.
Backed by womens' rights organisations, the petition had drawn more than 10,500 signatures online by Thursday afternoon.