When an employee files a sexual harassment charge with the employer, the employer, by law, must investigate that charge, even charges that appear to be without any merit.
Many employers take these types of accusations very seriously and have a policy of terminating those accused of sexual harassment, even without making a determination that this employee was guilty of anything. The issues of getting due process or being innocent until proven guilty beyond a reasonable doubt are concepts within the legal system, they are not requirements private employers must abide by.
Neither federal nor state laws protect a person who is accused of sexual harassment in the workplace because what the harassed may perceive as sexual harassment is subjective, and because the legislators consider sexual harassment to be a very serious charge. Without a union or employment contract, an at will employee can be terminated even when the termination is unfair.