Nthing in this article states or implies that union membership had anything to do with the decision to close the plant.  There's less farming going on here in favor of other development and traffic to Seattle is a nightmare cost wise.  

Union workers and non union workers lose jobs for a variety of reasons and there's little to no evidence that unionization leads to job losses at a greater rate than non union positions, Boeing is laying off non union workers in North Carolina too.  However deregulation and pro corporate tax policies tend to result in lower paying employment with higher turnover and job loss.  

Nice try though.