This may have been an injustice if your prosecution was based entirely on lies from your employer, but it's not a violation of your 4th Amendment rights. Your 4th Amendment rights prevent the government from unreasonable search and seizure. They do not apply to a private citizen or company, such as your employer.
The police do not need much evidence to make an arrest and the prosecutor doesn't need much to file charges or even to secure an indictment. All they need is something called "probable cause." Probable cause is just a reasonable belief that you may have committed a crime. As you can see, it doesn't take all that much to get the ball rolling. And the words of a believable complainant, even if he is later proven to be a liar, are enough to provide probable cause and get you charged. If you're thinking that anybody can get somebody arrested if they really want to badly enough, you're close to being right. Fortunately, however, more people are honest than not, so they don't play the system like that.
Police also play the system. You're not required to talk to them when they want to ask you questions or get information and documents from you. And they are not required to tell you the truth. The US Supreme Court has said that they can use deceptive and coercive means to learn about crime. So they sweet-talk you into thinking you are helping them, and meanwhile you are turning over information that leads to your arrest. They are allowed to do this, although they are supposed to warn you that anything you tell them can be used against you.
From there, however, in order to find you guilty of a crime, the state has to prove you guilty beyond a reasonable doubt. And you can have hearings on whether the police conduct was improper and confront the witnesses and the evidence against you. You do, as you have learned risk prison if you go to trial and lose. If they are offering you probation with a deferred adjudication (they'll dismiss the charges when you complete probation and make restitution) and you want to cut your losses, that's a fairly good deal. If you didn't commit the crime, however, you have an absolute right to turn down the plea offer and make the DA try to prove its case at trial.
Nobody will make you take a plea. Your lawyer may think it's a good plea and that a plea is a good idea for you. But if you are not guilty and want your day in court, you can refuse the plea. Then your lawyer is required to give you the best trial defense he is capable of giving you.