I'll try to give a brief crash course based on what I've read and what I've experienced. Massive "To the best of my knowledge..." before every single thing here.

Unions are intended to be an organised body of workers that typically elect a representative to bargain and speak on the group's behalf. The group voices desires, concerns, and problems to the representative(s) and the representative(s) try to help address those with the employer. Typically some sort of contract or agreement is negotiated and this becomes, of course, legally binding and enforceable.

Historically, unions have been for earning better wages and treatment in the workplace and, of course, began in skilled professions like carpentry, the railroad, electricians, etc. but nowadays largely includes "public sector" employees. Well-known unions today are teacher unions, police unions, firefighter unions, medical/paramedic unions, and even farmers.

While they are intended to be for the worker, and should be pushing for justice on behalf of the worker, some unions can become corrupt. They hemorrhage money from the members, claiming they owe excessive dues, fees, and other charges. They may neglect or ignore employee concerns. Some may even become politically involved and accept bribes, allowing that to determine their decisions rather than the employees they represent.

However, the power of unions has shown time and time again in earning the employees better wages, better working conditions, more structure, as well as power and security when using tactics such as striking or boycotting. Because of the ability for union organisations to become corrupt, it is so extremely important to research when looking to organise a union. Know what signs to look for, and what to be wary of.

This is where I get anecdotal - when I worked in a union job, I *did* have to pay union dues. I was making $15 per hour, working full time hours (40hrs per week). My union dues were taken directly from my paycheck and were approximately $15 per paycheck. I was still going home with my expected amount per paycheck (which I think was around $800 after everything?) By my understanding, union dues are supposed to be a small percentage of your wages and scale with your rate. You should not be paying even close to $100+ to be a member of a union.

For a brief (but still a bit wordy) rundown by somebody who has studied unions and been apart of one, unions were created formally to protect workers by giving them the power to negotiate and collectively bargain with their employer. Though it is hard to imagine, there was a point in history where people had first started working for wages and nothing was set in stone. In the US, the labor movement was responsible for certain benefits we take for granted nowadays, like an 8 hour workday and employers not being able to fire workers for becoming pregnant. For example, before workers collective demanded things like limitation on workdays, an employer could force a worker to work from sunup to sundown for pennies and if workers became permanently disabled because of unsafe working conditions the worker would be fired with no compensation or assistance with medical bills. Which obviously is not great for workers.

So the solution to those problems was for a majority of the workers to act together. Otherwise known as solidarity! The logic behind it is generally as simple as “they can’t fire everybody” and if they do fire everybody, the workers and the community band together to boycott, picket, seek legal reparations, and generally refuse to do business with that employer until the employer has to admit they were in the wrong and rehire those fired and agree to collectively bargain with them.

And yes, there has historically been known corruption in unions. However, that is almost entirely unlikely if we’re look into at the scale of individual Starbucks unionizing. With a small Union of less than 20 people (which is still a majority of their unionized store, I believe, though I didn’t double check so I may be wrong there) the payoff for anybody embezzling dues or accepting bribes is fairly low. Also, If you, a member of the union, are that close with your elected union leader, as in working with them constantly, there’s a much greater chance of them being held accountable and that you’ll either get to go to negotiation meeting with the company or if you have issues with what’s being negotiated, you can personally talk to your union president. Additionally, corruption tends to be seen in unions where the union board is their only job, as in the union president is ONLY the president and managing the union, not ever on the floor with the other workers, if that makes sense. If you want to know more about how unions have become corrupt in the past, I’d recommend looking into the Teamsters union corruption court case! So while yes, always be watchful to make sure you are being represented according to the amounts of fees you and your coworkers agreed on, in the case of a unionized Starbucks store at this point in time, I would say the risk is fairly low.

So ultimately, Pros: as a union, you’re going to have a say in your workplace. Your hours, your pay, benefits, working conditions, all of it. If anybody wants a run down on the grievance process I can certainly go into that, but long story short, if you’re unhappy with your hours, you’re being denied your legally guaranteed rights like breaks, you got shorted on your pay in some way, you’re being discriminated against etc, the process changes from you fighting those battles on your own to the union collectively addressing the company over it. How much anything changes is going to depend on how much Starbucks is going to bargain in good faith with their employees and thus we’ll pretty much have to wait and see on that. But another important thing! Right-to -work and At-Will states. For those, I’d recommend you look them up because you should always know your rights as a worker, basically, your employer can fire you at any time for any reason in states with those policies. HOWEVER, they cannot fire you without just cause if you are represented by a union. Any employee being fired has the right to go to the union and the union can argue their case and get them reinstated (many times with back pay) if it was unjust! I’m sure we could fill a whole thread with people who got fired for unethical reasons but ultimately there was no course of action because of the Right-to-Work, so having a union is protection against that.

Cons: in my opinion, the benefits of unionizing far outweigh the negatives because as a result of it being the work of a collective. if you are unhappy with something, chances are your coworkers are too and you take that to your union representatives and then talk with a company and figure out a solution. That being said, at the beginning of unionizing it is a difficult road. Employers will fire people for attempting to unionize. Wages are so low that most of us can’t even risk the couple weeks without pay. Also, if I’m being petty, nobody really likes having to pay dues like any other payment you have to make, because we would all rather have that money now even when we know it’s an investment for a better workplace. If I’m being cynical, there’s a chance the company will come down hard on a union, so it would be additional stress. And also, being part of a union means being prepared to go on strike. Strikes are where the union’s power comes from. The reason employers HAVE to collective bargain with a union is because of laws and also because of the threat that if they refuse the union can decide to go on strike, which in the case of Starbucks, would result in no income from that store and bad PR. Your union will only ever go on strike with a majority vote in favor of it, and even then, if you vote against it you technically CAN opt out of striking, those choosing to go to work would undermine your union’s power. but if you want to be part of a union going on strike is a thing you would need to be prepared to do, though most unions do not go on strike. unions do have funds and other programs to support workers through strikes, they aren’t easy.

Apologies for the length! I tried to keep it clear while providing context because I know a lot of people on this subreddit are new to employment and unions.

TLDR:
pros: a say in your workplace, better wages and working conditions, job security, being able to hold your employer accountable

Cons: union dues, employer retaliation, possibly going on strike