Not getting reinstated to old position after FMLA leave

I've been working at this company for a little over 4 years. I Got promoted to lead position about 8 months ago. My wife got pregnant, so I got FMLA and took time off from time to time to care for my wife, then after she gave birth I requested 3 months off through FMLA. I was approved. I came back to work early after 1 month and a half only to find that my position was given to the supervisor's brother in law. I texted my supervisor the next day asking if I'd be getting my position back. He responded saying that I did a great job as lead, but they're looking at a new approach moving forward and I will not be getting my position back. My company employs over 250 people, it is a union company. I have not contacted the union about this issue yet, but I plan to. Any advice? I'm at the point where I'm fed up with the company and I want to start looking for a new job.

 

My previous position. I was a regular CNC machine operator, I was promoted to working lead over CNC, Screw machine, and the production departments. After my leave I was demoted back to CNC machine operator.