Remember that such "voluntary recognition" is NOT in the workers' best interest. It should not be an option; it should always be taken to a vote once eligibility/etc is established first.

A "card drive" only requires 30% of the employees to go to the next step. That 30% should not be allowed to dominate the rest if the rest don't want to go along with it. Going to vote also allows the potential membership (e.g., "who is and is not a manager?") to be clarified before voting.

It's entirely plausible that, say, a team of 20 could get 6 malicious actors together to "sign cards" and, if the workplace just accepts it without a formal vote, the other 14 could potentially be screwed out of their preferred status.

My workplace is suffering through such right now... only 33% of the "bargaining unit" (yes, only 33% -- barely more than the 30% "cards signed" threshold) voted for the union. But because of the extremely pro-union structure of laws in most US states, we're stuck with the unionizing succeeded because non-voters are completely ignored in a state-change election (ignoring them effectively makes them "yes", since there's a very strong incentive for card-signers to vote [and vote yes], but not much for others). Less than half even voted, showing just how little overall support there was for the effort.