Can a non-union Kasson employee perform tasks under union contract?

At the Kasson City Council meeting March 23, whether or not a non-union supervisor may do work at the wastewater treatment plant was the topic of an animated discussion.
In a letter dated Feb 26, 2016, to Mark Schmitt, Director, Municipal Division of the state Pollution Control Agency in St. Paul, Mayor Steve Johnson wrote that Charlie Bradford “will have direct contact with the wastewater treatment facility three days per week for a minimum of two hours per visit.”
Bradford was promoted to the position of Public Works Director after the previous director retired in December. Before the promotion, he was a union employee at the wastewater treatment plant.
With the promotion, Bradford became non-union. At the meeting, council member Dan Eggler questioned if a non-union member can do the tasks of a union worker; that is, tasks at the wastewater treatment plant.
Eggler said that he had spoken to Schimtt about the letter and the appointment. 
He contacted Schmitt because, by a previously approved resolution, he cannot call the city attorney and the city administrator was instructed not to talk about the issue.
Eggler was also concerned because the decision was made without council input.
When city council members eliminated the city’s streets supervisor position last summer, grievances were filed by the Local 949 of the International Brotherhood of Electrical Workers against the city and arbitration is scheduled for April.
The question now is, will the union file more grievances against the city because a non-union employee has been directed to perform tasks that have been perceived to be union tasks?
It was decided to put the item on the next council agenda.
In other business, Chris McKern spoke to the commissioners about plans for the upcoming Festival in the Park, Aug 11 through 14 at the Veterans Memorial Park. He mentioned that the Fire Department Relief Association has been considering moving the Firemen’s Dance to the Park on one of the nights of the Festival.
Mayor Johnson said he was not in favor of that action. The dance would be too loud in that neighborhood. A liquor license would be needed, the area would have to be fenced, and more manpower would be needed to patrol the area, he said.
Council member Coy Borgstrom said he lives near where the dance now takes place – the fire hall on Main St. - and it’s fine in that location.  
This will be the 27th year for the Festival. McKern, as a volunteer, has spearheaded the festival since 2007.