There are three different things. Creating a new union where there was none before. Having a workplace's workforce represented by that union. An individual join

There are three different things. Creating a new union where there was none before. Having a workplace's workforce represented by that union. An individual joining a union. We can safely ignore the first of the three for your question (no one wants to talk about how the Teamsters union was formed) and the last one (a trucker fills out paperwork). For the second part, some employees work with an existing union to fill out cards indicating they want to join and be represented by that existing union. Once enough workers (by percentage) have filled out such cards, a vote is held among the affected workforce. (For instance, just the janitorial staff may have to fill out cards and vote to unionize the janitorial staff, or an entire Starbucks may unionize). The government sets regulations on the vote and/or oversees it, but both the company and the union get to make their cases in the time before the vote. Then, majority wins. (The company can just agree and start working with the union without the vote) Specific to your question about what a majority means, it certainly isn't by industry. I've heard of individual stores holding votes for Starbucks or Walmart, but also company wide votes for less retail oriented businesses. I'm not sure if that's because each location is a separate llc or because it can be by location. Everyone, regardless of vote, can then join the union or not. Some states prevent unions from negotiating an "only union employees" clause in their contracts, others do not. Note that even if it's "only union employees", that just means all employees must join the union for the term of their employment, not that they have to be a member to get hired at all.