Mass. Gen. Laws ch. 234A § 34
A trial juror shall have the right to one postponement of his term of juror service for not more than one year. The trial juror shall exercise this right by responding to the juror summons and indicating an election to postpone. The month, day and year to which such service is to be postponed shall be indicated in the response to the juror summons. The office of jury commissioner shall have authority to effectuate such first postponements. If the postponement date so designated is improper, unavailable or inconvenient for the court, the office of jury commissioner shall assign a date of service which is reasonably close to the postponement date selected by the trial juror. The jury commissioner, with the approval of the jury management advisory committee, shall have discretionary authority to limit the numbers of postponements allowed each day in each courthouse in order to maintain the integrity of the demographic cross-sections appearing in the juror pools.
Mass. Gen. Laws ch. 234A, § 34