A national union of nurses has accused members of the Service Employees International Union of physically assaulting some of its members at a labor conference in Michigan this past weekend.

The California Nurses Association/National Nurses Organizing Committee, an 80,000-member group affiliated with the AFLCIO, also charged SEIU members with stalking and harassing its members in recent weeks. On Saturday night, union officials said, about 800 SEIU members converged at a Dearborn, Mich., hotel and pushed their way into a conference organized by a labor magazine, Labor Notes.

“It’s disgraceful,” a spokesman for the union of nurses, Charles Idelson, said. “That is just unconscionable and inexcusable.”

According to witnesses, several hundred SEIU members forced their way into the hotel, shoving conference attendees. Witnesses said a 68-year-old woman, Dianne Feeley, was thrown to the ground and was taken to a local hospital to be treated for a cut on her head. “It was a scary situation,” the editor of Labor Notes, Chris Kutalik, whose arm was bruised during the skirmish, said. “It just seems ironic. The whole point of the conference was to promote unity.”

SEIU officials presented a different account, saying protesters were mostly women and children who gathered to demonstrate peacefully. Officials denied any physical assault on conference attendees.

The two sides disagree on the basis for the dispute. According to a spokeswoman for SEIU, Linda Tran, the California Nurses Association interfered with a labor vote in Ohio last month, ultimately preventing nurses from joining SEIU. She also said the union of nurses has a history of building its membership by “raiding” other unions.

Mr. Idelson said SEIU has wrongfully partnered with employers, making decisions that are not always in the best interest of its members.