You think the unions own the paper? The editorial board? I have news for you, if there is bias it's not coming from the people not in control. It's coming from the ultra-wealthy people who own these media outlets and I promise you they are not pro-union.
If the editorial board and these ultra-wealthy people want to stay on the good side of the news guild that all of their journalists are members of, then they have to be pro-union. They have to accept the very premise on which the laws that advantage unions were passed, which forces the employer to engage in collective bargaining with the union to the exclusion of all other parties.
The pressure for the management at news media companies to pander to unions on these issues is enormous and inescapable.
