Newspaper Aftonbladet reported that senior officials at the union and high-ranking members from other trade unions have been renting large apartments owned by Kommunal, the Swedish Municipal Workers' Union, at lower-than-average rents.
The apartments were operated by rental company Polstjärnan who kept the units off of Stockholm's official rental market queue so that they could be handed out to officials instead.
TT news agency also reports that one of the tenants was Swedish Foreign Minister Margot Wallström, who said she was misled by the union when she rented the property, which serves as her current home.
"They have given a completely false statement, and that is unacceptable," Wallström told TT, adding that she announced her plans to move out of the apartment on Thursday. "It hurts me and it hurts Kommunal."
At a press conference Friday, Kommunal's chairwoman, Annelie Nordström denied that the union had misled Wallström, saying that 'she must have misunderstood the information that she received from us'.
Aftonbladet also found that employees at Metropol Palais, a high-class restaurant operated by Kommunal through another company, transported boxes of wine to the union's own banquet hall in central Stockholm, which lacks a license to serve alcohol.
Alcohol sales and serving is tightly regulated by a government owned monopoly in Sweden.
On Thursday, the union's treasurer resigned over earlier revelations of extravagant parties, free spa weekends and the mismanagement of an unprofitable restaurant and conference center.
Chairwoman Annelie Nordström said Friday that she will not step down at this moment, adding that she wants to fix the situation before the union's next congress in May this year.