As well as promoting the events iconic Conde de God trophy, the models were also employed as umbrella assistants to players on court.
Those tasks required the women to work in the open, dressed in yellow mini skirts and short-sleeve T-shirts which featured a black Schweppes logo.
The women were denied a request to wear warm clothing on top of their uniforms because organisers wanted the Schweppes logo to remain the focus of the ensembles.
One of the models, who blew the whistle on the "sexual discrimination" told the workplace watchdog the conditions and uniforms resulted in many of the models getting sick.
"Me and my colleagues almost every night had fevers because we left the matches already with a fever," one of the models said in a public statement issued in Spanish.
"I left with migraine and fever from the matches.
"It was working in conditions in which you teeth chattered."
The same woman said after the tournament: "We are always girls, girls, miniskirts and showing flesh".
"The fact is that we could not wear the jacket because the brand could not be seen, it is also in the umbrella, the dress has to be seen, and if we are cold it is the same."
An investigation launched into the claims made by eight models has now been concluded by Catalonia's regional Work Inspectorate.
The claims of the eight models were registered with Spain's General Workers Union (UGT), who then pushed for the Catalunya authority to take action.
"Unfortunately, UGT-Catalunya has not been wrong," the UGT said in a statement issued in Spanish.
"The Work Inspection has been able to see what everyone saw and we denounced — the use of the body of eight women as advertising in the Conde de Godo Trophy contest of Barcelona, and also the lack of guarantees of the preventive activities in work hazards risks for the female workers from Barcelona's Tennis Real Club."
Union secretary Eva Gajardo told Spanish TV the union strongly condemns using the bodies of female models for promotional purposes.
"We are used to seeing scenes where women are put in situations where they have to show some flesh," she said, according to El Pais.
"Work inspectors have seen what everybody else saw, the bodies of eight women used as advertising gimmicks for the benefit of the Conde de Godo tennis event,"
Schweppes and the Tote Vignau agency have both been slapped with fines of more than $38,000 (€25,000), but further action can still be taken by the industry authority.
Fines for breaches of sexual discrimination workplace rules range between $15,000 and $287,000.
Officials for the ATP Tour and tournament organisers at the iconic Barcelona tennis club, where the tournament was held, say they did not know about the working conditions of the hostesses.
Barcelona's Royal Tennis Club has been warned that it must: "fully guarantee that occupational safety and workplace health legislation is fully enforced in future Conde de Godo tennis events".
However, no further action has been taken against the tournament.
Schweppes and Tote Vignau are yet to indicate if they will appeal the workplace watchdog's action.
ATP tournament organisers also apologised in November for a ceremony involving female models provocatively revealing the letters "A" or "B" to determine the draw for the ATP's Next Gen Finals tennis tournament.
The ceremony was supposed to highlight Milan's status in the fashion industry.
"The intention was to integrate Milan's rich heritage as one of the fashion capitals of the world," the ATP and sponsor Red Bull said in a statement.
"However, our execution of the proceedings was in poor taste and unacceptable. We deeply regret this and will ensure that there is no repeat of anything like it in the future."
Earlier, two-time Grand Slam champion Amelie Mauresmo tweeted, "Disgrace," while Andy Murray's mother Judy added, "Awful."
Players were asked to select models who then revealed an "A" or a "B" to determine which group they will play in. One model pulled up her dress to reveal an "A" on her right thigh.
The Italian tennis federation declined comment, saying the ATP organised the draw ceremony.
— with AP
