Fourth of July weekend has been dubbed a "no-refusal" weekend. That means that if you are pulled over, a judge is likely to be in a mobile vehicle and may sign a warrant stating that a needle can be jammed into your elbow to draw your blood for an alcohol analysis.
The Bill of Rights guarantees that you have a right to privacy. The 4th amendment protects you against warrantless searches and seizures
. Normally, unless you consent to the blood draw or breath test, the police do not take a specimen. However, if a judge signs a blood warrant, the fourth amendment typically doesn't come into play as long as the judge had cause to sign the warrant.
However, just because you give a blood draw does not mean you will be convicted. The timing of the blood draw is critical. Just because your blood alcohol content was above the legal limit an hour or two after the time you were driving does not mean your BAC was over a .08 when you were driving.
Your blood absorbs and eliminates alcohol at a strange pace. While you continue to absorb alcohol up to 1.5 hours at a rapid pace, you eliminate alcohol very slowly.