With labor making a bid to unionize the financial services sector, management should proceed with the utmost delicacy. The National Labor Relations Act is almost exclusively a list of "don'ts" applied to management with very few restrictions applied to union organizers. Management will be playing defense throughout the workplace organizing process. That's just the way it is.
Nothing has improved on the original defense against union organizing efforts pioneered by automobile magnate Henry Ford in the 1920s. Ford's tactics were: Pay your employees well (at least the industry standard, if not higher); provide them with good benefits and a safe work environment and keep an ear open for any concerns they might have. Do those things and it is unlikely workers will see any need for a union.
It is important to do these things proactively. Be generous to workers when times are good and all appears well. You should consider it a long-term investment in the stability of the company. It will also help attract and retain skilled workers. Don't wait until reports of discontent start rearing their head. Make a point of regularly interacting with employees. An "open door" policy doesn't help if workers are uncertain whether they can truly walk in and raise a concern with their boss at any time. A manager that is visible and engages them in casual conversation is much more likely to hear concerns before they metastasize.
However, all of the above may not prevent an organizing bid from happening. One favorite tactic of unions is called "salting," which is sending an undercover agent to apply for an open position at a workplace. Organizing of any sort is a protected activity under the NLRA, so firing a worker for that is a violation of the NLRA. The fact that the worker may have applied for the position in bad faith is irrelevant. But there has to be genuine discontent at a workplace for a salt to be effective.
The National Labor Relations Board generally doesn't take management's intentions into account. The standard is that any action by management that can reasonably be interpreted by a worker as a threat is a violation. An inadvertent error by management is considered just as bad as a malicious one and can just as surely result in a sanction. A threat to employees along the lines of "X will happen if you unionize" is a violation of the NLRA. So is a promise along the lines of "I'll give you a raise if you don't unionize." Both are deemed as interfering with worker rights. Questioning workers about why they want a union is generally seen as inference too.
Managers may not engage in "surveillance" of union activity either. This is a bit grayer in the era of social media. The dividing line is generally whether something is put out publicly (such as a website anybody can click on) or is something that is not immediately accessible (such as a website that requires signing up for access).
So what can management do? Management can explain. They can describe what union contracts are and what they do. They can describe how the NLRA works in practice. They can describe how the law gives unions power and authority over employees. At this stage, management pretty much has to hire outside consultants to explain these things to workers. There's too many ways it can go wrong if management tries it on its own.
The NLRA officially kicks in when the union begins soliciting workers to sign forms saying they want to be represented by the union, a process dubbed "card check." A union with 30% of the workforce signed up can insist the NLRB hold an election. A union with more than half of the workforce signed up can present the cards to management and demand it recognize the union automatically. Unions can and sometimes do forge the signatures. If things look suspicious, management can request that the NLRB oversee an election to determine if workers really want representation.
As with political elections, the winner is whoever gets the most votes regardless of how many votes are cast. If a workplace has 100 workers but only three actually vote and two of the three vote for the union, then the union wins. Management should insist on an in-person vote at the worksite as opposed to a mail-in ballot. This will ensure the highest turnout. In mail-in elections, activists are the ones with the most inclination to fill out a ballot. Those not in favor of a union are more likely to toss out the ballot on the mistaken assumption that it is junk mail or a scam or simply forget to mail it.
The bad news is that if things have progressed to the stage of an election, management has probably already lost. Unions typically wait until they have well more than half of the workers signed up before they make a bid for representation. Bloomberg reported that unions won 76% of the NLRB-monitored elections held in 2022.
Thus, the best way to win is to ensure that the workers have no reason to be upset enough to unionize in the first place.