In the State of California, all requests to be excused from jury service that are granted must show the court undue hardship or (recent) previous jury service

All requests to be excused from jury service that are granted for undue hardship must be put in writing by the prospective juror, reduced to writing, or placed on the court's record. The prospective juror must support the request with facts specifying the hardship and a statement why the circumstances constituting the undue hardship cannot be avoided by deferring the prospective juror's service.

Reasons for excusing a juror because of undue hardship

An excuse on the ground of undue hardship may be granted for any of the following reasons:

(1) The prospective juror has no reasonably available means of public or private transportation to the court.

(2) The prospective juror must travel an excessive distance. Unless otherwise established by statute or local rule, an excessive distance is reasonable travel time that exceeds one-and-one-half hours from the prospective juror's home to the court.

(3) The prospective juror will bear an extreme financial burden. In determining whether to excuse the prospective juror for this reason, consideration must be given to:

(A) The sources of the prospective juror's household income;

(B) The availability and extent of income reimbursement;

(C) The expected length of service; and

(D) Whether service can reasonably be expected to compromise the prospective juror's ability to support himself or herself or his or her dependents, or so disrupt the economic stability of any individual as to be against the interests of justice.

(4) The prospective juror will bear an undue risk of material injury to or destruction of the prospective juror's property or property entrusted to the prospective juror, and it is not feasible to make alternative arrangements to alleviate the risk. In determining whether to excuse the prospective juror for this reason, consideration must be given to:

(A) The nature of the property;

(B) The source and duration of the risk;

(C) The probability that the risk will be realized;

(D) The reason alternative arrangements to protect the property cannot be made; and

(E) Whether material injury to or destruction of the property will so disrupt the economic stability of any individual as to be against the interests of justice.

(5) The prospective juror has a physical or mental disability or impairment, not affecting that person's competence to act as a juror, that would expose the potential juror to undue risk of mental or physical harm. In any individual case, unless the person is aged 70 years or older, the prospective juror may be required to furnish verification or a method of verification of the disability or impairment, its probable duration, and the particular reasons for the person's inability to serve as a juror.

(6) The prospective juror's services are immediately needed for the protection of the public health and safety, and it is not feasible to make alternative arrangements to relieve the person of those responsibilities during the period of service as a juror without substantially reducing essential public services.

(7) The prospective juror has a personal obligation to provide actual and necessary care to another, including sick, aged, or infirm dependents, or a child who requires the prospective juror's personal care and attention, and no comparable substitute care is either available or practical without imposing an undue economic hardship on the prospective juror or person cared for. If the request to be excused is based on care provided to a sick, disabled, or infirm person, the prospective juror may be required to furnish verification or a method of verification that the person being cared for is in need of regular and personal care.

Excuse based on previous jury service

A prospective juror who has served on a grand or trial jury or was summoned and appeared for jury service in any state or federal court during the previous 12 months must be excused from service on request. The jury commissioner, in his or her discretion, may establish a longer period of repose.

Source: http://www.courts.ca.gov/cms/rules/index.cfm?title=two&linkid=rule2_1008