Wikimedia Foundation refuses voluntary union recognition, hires union-busting law firm

From reading the article and watching the video, it didn’t sound like they were refusing the option of having a union. It was more that they wanted to have an official vote on the matter, and didn’t want to be pressured into a decision on the spot:

[W]e believe a secret-ballot election conducted by the National Labor Relations Board is the appropriate path forward. This process protects individual choice and ensures that any outcome reflects the collective will of those eligible to participate.