You're asking whether you can legally be retaliated against for raising an employment concern in good faith. As much as I'd like to be able to tell you it would never happen, the reality is that unethical employers sometimes do retaliate illegally. It's therefore important to know whether you are covered by any anti-retaliation policies and laws for your workplace, jurisdiction, and the issue that you're complaining about.
Here are a couple of things to consider:
Large employers typically have important anti-retaliation language embedded in specific company policies. Therefore, the first place to check would be your company policy manual, intranet/portal, etc.. Read, understand, and save a copy of relevant company policies. If your employer has no workplace policies, that's a big ole red flag.
The second place to check would be your employer's labor law postings bulletin board. It's typically located in easily accessible locations to all employees as well as applicants, such as in the HR front office. You may learn that you have rights you didn't know you had by simply reading this bulletin board. People overlook this resource, but it's important.
The size of your employer determines whether you are covered by certain federal and state employment laws; some laws pertain to employers with 15 or more employees, others laws to employers with 50 or more workers, for example. Therefore, the issue that you are complaining about matters. People who work for small businesses are often sorely disappointed to discover how employer size negatively impacts their rights.
It's also assumed that you're making the complaint in good faith because you genuinely believe it to be a problem rather than you simply want to be a nuisance.
If you are concerned about being fired, you may want to consult an employment attorney in your jurisdiction about your specific complaint.