First, Warrants are more effective at obtaining blood, breath, and urine test results than criminalizing refusing a breath test. There is evidence in many states that criminalizing refuses had the effect of increasing refusal rates.
Second, Because of the widespread availability of electronic (email and video conference warrants) and telephonic warrants criminalizing DUI refusals is unnecessary.
Third, the threat of criminal incarceration for refusing a DUI blood, breath, or urine test is coercion and violates both the spirit and letter of the 4th Amendment.
The bottom line is that the exercise of a Constitutional right should never be a crime. A decision is expected in the fall. SCOTUSblog did a pretty thorough review of the arguments as well.
-Author: George C. Creal, Jr.