A powerful Las Vegas labor union said Thursday that staffers of the Bernie Sanders campaign wore union pins in order to gain access to employee areas at four of the city's unionized hotels.

Culinary Workers Union Local 226, an affiliate of Unite Here, said it was "disappointed and offended" by what it suggested was an unethical move by the Vermont independent's campaign. The union, powerful in Nevada politics, hasn't yet endorsed a candidate in the presidential race, and the Democratic candidates have all been wooing the union in hopes of securing its support.

The union said it believes the Sanders staffers wore the pins in order to access to the same employee areas that union staffers visit. Jon Ralston reported Thursday that Sanders staffers were "masquerading" as members of the culinary union.

"It's completely inappropriate for any campaign to attempt to mislead Culinary Union members, especially at their place of work," Geoconda Arguello-Kline, secretary-treasurer for the union, said in a statement. "The Culinary Union button that hundreds of thousands of union members have proudly worn to work every day represents 80 years of struggle and fighting for justice."

The Sanders campaign told CNN that staffers "did wear Culinary buttons to try to talk to workers, but did not misrepresent who they were." That may well be true, but from the vantage point of the union that may not matter.

Companies and unions sometimes negotiate certain spots on company property where union staff can freely go to talk with the employees they represent -- in this case, particular areas in the employee dining halls. This is a valuable privilege that unions take seriously and wouldn't want to jeopardize. Unauthorized visits from political outsiders could potentially do that.

A Sanders spokesman did not respond to a request for comment.