The National Labor Relations Board is an independent federal agency vested with the power to safeguard employees’ rights to organize and to determine whether to have unions as their bargaining representative. The agency also acts to prevent and remedy unfair labor practices committed by private sector employers and unions.
Why do Americans need the employers approval to form a union? Or for what are they waiting?
They don’t - this is about a deadline for the employer to voluntarily recognise the union as the entity representing their workers.
If that doesn’t happen, as may be the case here, the union can go to the NLRB to hold a ballot and, eventually, force the company to recognise them.
Basically, they gave WotC the easy option first but they ignored it.
Strange, but OK. Has an employer in the US ever voluntary accepted a union?
Yes
Additional context:
NLRB = National Labor Relations Board
https://www.nlrb.gov/about-nlrb/what-we-do