Can you be dismissed from a graduate program for attending jury duty? From what I’ve read, an employer can’t legally fire you for attending jury duty, although they don’t have to pay you.

I’ve been called before but never had to serve more than a day.  However, a grad student friend of mine was called, had already deferred once before, and is concerned that if he has to serve for an extended period, it would set his work back so that he couldn’t graduate in time, and his department told him that he can’t request another extension.

Can you be dismissed from a program for fulfilling your civic duty?

This is in the US, and the university is public if that has any bearing.

* UPDATE * - I'm really glad that I asked this question.  Today I received a summons for jury duty, and I am to appear in court at the EXACT date and time of my defense.  It can happen to you!!!

* UPDATE 2 * - Here is how I dealt with it.  I told my advisor that I had been called and asked if he would contact someone in the university administration to write an official letter asking to excuse me from jury duty on that day.  A few days later, I was given a letter to that effect.  The county I live in has a Jury Commission where you can go and "plead your case" to be excused.  I went to the Jury Commission and brought my letter, at which time they asked me when I would be able to serve.  I gave alternate dates (after my planned deposit date ;-) ), which they accepted.  The Jury Commission really appreciated that I had brought an official letter from the administration, as they had received excuse letters from doctoral student's advisors, and rejected them.  Having something from the university administration itself carries much more weight.  Thankfully, it all worked out!
Serving on a jury is considered a crucial civic duty - I think it would be extremely damaging for any university to directly or indirectly punish a student for serving on a jury.

That said, it is possible that an institution could disagree with how much jury duty impacts your friend. It would be quite another thing for a school to dismiss a student because they missed a specific date of class, but that is different than a project that is worked on over years. That is, they would not be dismissing them for participation as a juror, but for insufficient progress during all the other time they didn't spend on a jury, deciding that the time spent on a jury was not substantial enough to impact performance. Serving on a jury for 1 week wouldn't require a university to give another semester-long extension.

Assuming you are referring to the U.S.: it might depend on your local government, but it can be possible to defer more than once or to be excused entirely if the courthouse agrees. There is often a limit but in places I have lived it was not limited to once. 

Usually the phrasing for getting deferred is something along the lines of "undue hardship" or "extreme inconvenience" which certainly applies to a graduate student nearing the end of their program.

If your friend can't defer and has to report, there are also at least some anecdotes and rumors that academics are likely to be rejected from juries for a number of reasons, though I am not aware of any social scientific study of this phenomenon. I would also add that long jury service for anyone is pretty rare - most court cases are fairly simple, and jurors may not even serve on a case if they are not selected or there is not a large number of jury trials during the time of service.

I am not aware of laws that protect grad students specifically, but this is really a question to ask a lawyer rather than Academia.SE. There might be local laws that effectively count grad students as protected employees, but I think it's likely to be a gray area due to the temporary and not-really-employee status of grad students. More likely, your institution or graduate school has some of their own policies regarding jury duty - I would suggest you or your friend consult those policies.