The clash within the union members took place over the president's post, Mansa Senior Superintendent of Police (SSP) Viveksheel Soni said.
The victims have been identified as Raj Tejinder (26), a dismissed constable of Haryana Police, and Raju (25), he said.
A person was also injured in the incident and had been hospitalised here, Soni said.
Police have registered a case in this connection and started investigations.
No arrests have been made so far, he said.