If a driver is impaired by drugs or alcohol when he or she is operating a vehicle, it is against the law. This is because they are at a much higher risk of making an error of judgment, are subject to delayed reaction times and are more likely to engage in reckless or distracted driving. In order to enforce this law, drivers may be stopped and asked to take a Breathalyzer test, which can determine the level of alcohol in their blood.
A Breathalyzer test is not the most accurate way to test the blood alcohol concentration (BAC), but it is the most convenient, and it allows field sobriety tests to be conducted. They are usually conducted by a police officer, and they likely have a reason to believe that the driver is under the influence of alcohol; perhaps he or she was speeding or jumped a stop light.
The implied consent law applies to all states, and it means that by choosing to be the driver of a car, you have already given consent to partaking in a drug or alcohol test at request. Therefore, if you refuse to take any test upon request, you are breaking the law and also give the impression that you are guilty of driving under the influence.
If you have refused to take an alcohol or drug test, you will likely have your driver's license confiscated and your driving privileges suspended. It is important to take action immediately if you have been involved in such a situation, so you can work towards getting your license back as soon as possible.
Source: Findlaw, "DUI offense basics," accessed Oct. 20, 2017