An investigation by newspaper Dagens Nyheter (DN) published on Monday found that many trade unions forbid members of the Sweden Democrat party (Sverigedemokraterna, SD) from taking official positions - which are otherwise elected offices.
While one union chairman said unions which do not do so are "weak", a political scientist said the situation presents a challenge for democracy.
The investigation found that six of the 14 affiliates refused to grant a position to Sweden Democrat members, even in politically independent associations.
"SD's politics contravene our by-laws," Transport union chairman Lars Lindgren told the paper. "One can't represent those politics and our members simultaneously."
The numbers were even more dramatic for the Swedish Trade Union Confederation (LO), which has strong ties to the Social Democrat party. Twelve of the 14 LO unions banned Sweden Democrat members from having an official position.
Ann-Katrin Löfwenhamn was a board member of Unionen, one of Sweden's largest unions, in Dalarna for two years. But when her political views were discovered, her job was made difficult for her, she claims. She left her position two weeks ago.
"It was my own choice," Löfwenhamn told DN. "I need some peace and quiet. I sat on the board of directors for two years and did a good job. But as soon as they heard that I belonged to SD, I no longer had the right values according to certain people. It's ignorance on their side."
Ann-Cathrine Jungar, a political scientist at Södertörn University in Stockholm, said that the trade unions' behaviour was an extension of the governing parties' choice to exclude SD from negotiations - but that such methods were likely to backfire.
"There is a democratic problem when members cannot be represented by those they choose," Jungar told the newspaper. "It strengthens the party's image of being antagonised by the establishment."
Lars Lindgren however disagreed.
"If you don't take a position for everyone's equal worth, it's like saying you can just take your members' money and forget about the rest. It's cowardly."