It's pretty lame to put out a one sentence implication that unions are the reason for the downfall of this 127 year-old business without, you know, any actual proof or data or argument for that being so. The only sentence in the actual article hinting at why they closed links it to falling sales starting in 2016, and the general state of the economy.
The employee unionization was likely a result of the cost-cutting measures being implemented on their backs, meaning the business was already failing.