Detroit area SEIU at Bay City parade?

I went to the anual St. Patrick's Day parade in Bay City this afternoon and was quite shocked to see the SEIU marching. I'm trying to find out if this was actual grassroots support or were these people bussed in from Detroit where SEIU is headquartered?

Maybe it was all those adult care workers who were forced to join the SEIU in order to receive payments from the state. I am sure they were showing their support