In the United States, the jury system is one of the means by which the civil authority maintains the safety of the general population. It is one of the ordinary duties of citizenship and participation in a free and orderly society to do one’s best to fulfill the obligations of jury duty when called upon to do so. Deliberately skipping jury duty without just reason could well constitute grave matter. For guidance on discerning the gravity of this action, I recommend discussing it with your confessor.